Modified oxide-coated aluminum and the method of modifying

Id

Id to id X to Id Q

Q Z z 4 id

March 19, 1968

Id ijZ xo

Id

l. j. weber 3,374,155

MODIFIED OXIDE-COATED ALUMINUM AND THE METHOD OF MODIFYING

Filed Feb. 19, 1965 o

p to to id to

X id h

5o

Id ως zuj<t «

44° Z ζ_ω to _m< id x

Id to ω S e

X to. Ιϊω

Id t

U-« I oao = on g-S 0^2 Zto₃-2o«l

35? OX® Id OCJ

Id

Id O to p?o to

Id — o to «2 to X o to id Z to to id χιο x °IO° x2 to = -X to uj t²x —*« id

Id

Id to to id to id

Id id^

XId o

Id to

Z

X

O to to id X id to to

X id o 2 to

NOT* ΓΗ2

XX$2

C4 Q O ¹ Z . .

2^ω ZOT?

Old -* .Sz

So id X id^O tK to ^< to ο Ο X id δ « i=2g o to to o o Id ZD O

Z I o 0>

J, 2 id

X id o

to id to z

X id to

Id2ld

2 to <

X to UJ o ox id O

ΛΙ > • 4 tox is t-P id X to

U.OT °2 z = O to Γ to

OTq, to O

OO

INVENTOR.

LCfOW/G j: WEBER

BY

<img file="US3374155A_D0001.tif" />

Jrr0RiVE&gt;&amp;

United States Patent Office „ , „ ^{3 374 155}

- Patented Mar. 19, 1968

3,374,155 MODIFIED OXIDE-COATED ALUMINUM AND THE METHOD OF MODIFYING

Ludwig J. Weber, 6016 Birch Crest Drive, Minneapolis, Minn. 55424 Continuation-in-part of application Ser. No. 397,018, Sept. 16, 1964. This application Feb. 19,1965, Ser. No. 434,121

Claims. (CI. 204—38)

ABSTRACT OF THE DISCLOSURE

A process of improving the corrosion resistance of aluminum articles that includes removing the impurities from the article surface, then chemically or electrolytically forming an artificial aluminum oxide coating, treating the artificially oxide coated article to a dilute aqueous solution of an inorganic base such as NaOH or KOH, and thereafter treating the article to an alkaline silicate solution. Advantageously intermediate the above mem tioned treatments, the article is treated to one or more of aqueous solutions of (1) organic compounds having cations of various iron group metals and anions of acetates, citrates, oxalates, tartrates, (2) organic compounds of various alkali and alkali earth metals having anions of acetates, citrates, oxalates, (3) ammonium hydroxide, (4) ammonium compounds having an anion of such acetates, citrates, carbonates, and (5) various mixtures of the above.

This application is a continuation-in-part application of my application Ser. No. 397,018, filed Sept. 16, 1964, and now abandoned.

This invention is directed to treating aluminum to form a modified oxide coating thereon that substantially increases the corrosion resistance above that obtained with conventional aluminum oxide coatings. More particularly this invention is directed to forming an aluminum oxide coating on aluminum, then activating said coating and then subjecting the activated coating to further treatment to provide a highly corrosive resistant coating.

In order to facilitate the description of the invention, the following definitions are applicable unless from the accompanying description the terminology is clearly used in another sense. “Oxide coating” refers to a coating that is substantially composed of aluminum oxide on the surfaces of aluminum or various alloys of aluminum. Such “oxide coatings” may be produced by various methods that comprise a chemical or electro-chemical reaction between the aluminum surface and a solution of a chemically active substance or substances, but are not deemed to include an oxide coating on aluminum resulting from ordinary atmospheric oxidation. The term “aluminum” includes aluminum per se and its various alloys; while a modified oxide coating” refers to coating formed by treating aluminum to first form an oxide coating and then further treating an oxide coated aluminum as set forth hereinafter to substantially increase the corrosion resistance over and above that obtained from only forming an aluminum oxide coating.

The protection of metals from corrosive influences is constantly a problem to the manufacturer as well as to the user. Various materials and procedures are being used at the present time but the search for improvement is going on constantly in order to increase the useful life of the products made from metals. Aluminum has many applications and its use could be greatly increased if the resistance to corrosive mediums could be improved.

Oxide coatings on aluminum and its alloy can be readily applied by chemical and electrochemical means. Even exposure to the ordinary atmosphere produces a protective oxide film. This oxide coating is actually integral with the metal so that it will not peel like paint or plastics which are so commonly used for the protection of metals.

An oxide coating which may be formed on aluminum by an anodic process using, for example, sulfuric acid as the electrolyte has many advantages such as increased hardness, good appearance, non smudging, resistance to mild corrosive solutions and others. It has, however, these 10 disadvantages which seriously limit its usefulness, namely:

(1) The oxide coating is soluble in caustic solutions such as sodium hydroxide, sodium carbonate and sodium, phosphates which are used in detergents for cleaning various types of equipment like cooking utensils, dairy 15 equipment, clinical ware etc. Usually the cleaning in commercial installations is done by automatic machines in which the solutions are set at a temperature of 160 to 180° F.

(2) The oxide coating is subject to deterioration by 20 hydration when exposed to moisture. This action increases as the temperature of exposure increases.

(3) The oxide coating is also attacked by comparatively weak acid solutions.

In accordance with this invention it has been found 25 that by proper treatment of the aluminum oxide coating formed by chemical or electrochemical methods, these disadvantages can be overcome, and thus allowing aluminum to be used in many applications where resistance to corrosion and deterioration is required.

One of the objects of this invention is to provide a new and novel process of treating aluminum to form a modified oxide coating of other stable compounds in order to obtain, a substantial increase in corrosion resistance of the oxide coating obtained by present procedure. Another 35 object of this invention is to provide a new and novel activation treatment of oxide coated aluminum prior to exposing said aluminum to a silicate treatment with or without subjecting the article being treated to intermediate treatment including various solutions of organic com40 pounds of alkali, alkaline earth and iron group metals in the process of forming a modified oxide coating. A further object of this invention is to subject aluminum to a new and. novel coating treatment that provides a coating very resistant to caustic and salt solutions as well as 45 overcome the action of hydration.

An additional object of this invention is to provide a new and novel process for treating aluminum to obtain a substantial, increase in corrosion resistance of the oxide coating obtained by present procedures that includes acti50 vating the oxide coated aluminum, treating the activtaed oxide coated aluminum to a solution of an ammonium compound which readily releases ammonia or ammonium hydroxide and then to an alkaline silicate treatment.

Other and further objects are those inherent in the 55 invention herein illustrated, described and claimed and will be apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the 60 claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the invention may be employed.

With reference to this disclosure an explanation of ^b5 terms used is pertinent as follows:

(1) Sulfuric acid electrolyte: sulfuric acid concentration of 15-18.5% current density of about 12 amperes per square foot, and a temperature of electrolyte solution _7Q about 70±2° F.

(?) Chromic acid electrolyte: chromic acid concentration of 10%, current density of one to three amperes per

3,374,155 square foot, 40 volts and a temperature of solution of about 65° F.

(3) Hard coat: sulfuric acid electrolyte having a sulfuric acid concentration of 7%, current density of 30 amperes per square foot, and the temperature of solution ₅of about 25° F.-35° F.

(4) Alrok: trademark of the Aluminum Company of America, wherein a coating on aluminum is formed by a chemical treatment of (a) 2% Na₂CO₃ and 0.1% K₂Cr₂O₇, (b) 3% and 0.1% respectively or (c) 0.5 and _J01.0% respectively in water at a temperature of 175° F212° F. (ratio of carbonate to dichromate being from 20 to 1 to 30 to 1) depending on the product being treated; rinsing in water and which can be sealed in a solution of about 5% K₂Cr₂O₇ at about 180° F. to 190° j5 F. with an original pH of 4.5 to 5.0.

(5) Iridite: proprietary name for a powder of 61.7% ammonium phosphate, 22.9% ammonium fluoride and 15.4% potassium dichromate that is put in solution for chemically forming a phosphate conversion coating on 20 aluminum.

(6) *FeNH₄C an abbreviation used at various places in the specification to designate ferric ammonium citrate.

(7) *NH₄C an abbreviation used at various places in the specification to designate ammonium citrate. 25 (8) Liquid G.T.W.—an arbitrary non-proprietary designation used for a non-trademarked liquid sodium silicate having a ratio of percent Na₂O:percent SiO of 1:3.25 which is produced by Lyons Chemical, Inc., of St. Paul and distributed by Geo. T. Walker Co., Inc., of Min- 30 neapolis, Minn.

The normal compositions of the aluminum alloys appear in the table below:

NORMAL COMPOSITION 1 _----------------—-------- 35

Alloy Copper Manga- Magne- Chro-Zinc nese slummium

1100-._____ (99.00 percent minimum aluminum)

3003_______________..... 1.2 ------------------------5005 0.8

5052 2. 5

5357________ (²) 0.31.0

5457________ (²) .301.0

7075________ 1.6 .32.5

High

Purity,... 99.99 -----------------------------------------------¹ Percent of alloying elements—aluminum and normal impurities constitute remainder. 45 ².29% maximum silicon and iron, 0.2% maximum copper.

³.18% maximum silicon and iron, 0.2% maximum copper.

&lt; Aluminum.

. All of the below listed silicates are listed by their trademarks, the trademarks being those of Philadelphia Quartz Company, Philadelphia, Pa.:

Ratio percent

Trade Name Type K2O:percent

SiO₂

Ratio percent NaiO:percent SiOj

Kassil #1_________

G. D_____________

N________________

8-35______________

Metso 55_________

Metso 99

KsSiCh 1:2.50 ------------NaSiOj __________________ 1:2.00

NaSiOj __________________ 1:3.22

NaSiOi __________________ 1:3.75

Metasilicate plus other detergent material Sodium sesqulsilicate hydrated

The procedures hereinafter outlined and described consist of modifying aluminum oxide so as to change it from a product that is readily attacked to one that resists the attack of solutions that are very corrosive to aluminum as well as conventional oxide coatings that are presently employed.

First a brief description of a preferred procedure including a preferred form will be set forth in order to facilitate an understanding of the invention and then the invention will be more fully described including alternate procedures. This includes starting with a clean aluminum sheet or other aluminum articles which is provided with an aluminum oxide coating by an electrochemical procedure using sulfuric acid (15-18.5%) as an electrolyte and the aluminum sheet as the anode. A current density of 12 amperes per square foot with varying lengths of time is used in applying the coating. The sheet is then rinsed in water.

The next step which appears to be the most important for obtaining best results is to activate the oxide formed on the aluminum sheet. This is accomplished by heating the oxide coated sheet at about 212° F. for 5—15 minutes in a solution of about 0.2 to .55 gram sodium hydroxide or potassium hydroxide per liter of water.

The activated sheet is then exposed to a solution of an organic compound of the iron group metals or to either ammonium hydroxide or ammonium citrate. Best results are obtained using about 5 grams of nickel acetate and 5 grams of ferric ammonium citrate in a liter of distilled water, heating for 15—30 minutes at 140-165° F. and then rinsing the thus treated aluminum sheet in water; or using .5-5 cc. concentrated ammonium hydroxide per liter of water at about 200-212° F. for about 15-20 minutes, or using about 9-10 grams of ammonium citrate in a liter of water at about 200-212° F. for about 15 minutes.

The thus coated aluminum sheet is exposed to an organic solution of an alkaline or alkali earth metal. Preferably a solution of 10 grams per liter of magnesium acetate or potassium acetate at about 212° F. for 30±10 minutes is used and then the thus treated sheet is rinsed with water. Finally the above coated sheet is exposed to a solution of about 27 cc. potassium silicate, Kassil #1, in a liter of distilled water at about 212° F. for 30 minutes to form a spinel type compound, rinsed with water, dried and then buffed to remove any loosely adhering film.

Desirably all solutions are made up using water low in mineral constituents and near neutral; and preferably distilled or deionized water.

Finishing and treatment prior to the application of the oxide coating

The finish or appearance of the oxide coated specimens depends to a great extent on the surface condition prior to the application of the oxide coating. In order to obtain best results, the aluminum should be substantially free of foreign material, including any scratches or metal defects, dirt, oil and grease and any substantial coating formed by air oxidation, both before applying the oxide coating and thereafter. The proper surface finish can be obtained by proper procedure in rolling the sheet, buffing or other mechanical finishing methods.

The aluminum to be treated is cleaned, for example, by 50 one or more of the steps as follows:

(1) Degrease in vapor degreaser, (2) Degrease as in (1) followed by caustic etch, (3) Degrease as in (1) followed by bright dip, (4) Degrease as in (1) followed by caustic etch and bright dip.

Tests, examples of which are set forth hereinafter have shown that the condition of the sheet free from scratches and other defects with a finish “as rolled” “buffed” and etc., or the various chemical treatments of the above θθ steps had no substantial effect on the corrosion resistance of the final (modified) oxide coating.

Part 1.—Aluminum oxide produced by electrochemical means

Aluminum oxide coatings can be produced by electrochemical methods using an oxidizing acid as electrolyte and making aluminum the anode. Acids which can be used are sulfuric, chromic, sulfamic and oxalic although 70 mixtures of these as well as other acids and compounds may also be added to these in order to obtain certain desired characteristics as hardness, color or texture. Sulfuric and chromic acids were selected for the majority of the specimens set forth herein as they are the ones 75 generally used in this country.

(1) (2) (3) (4)

15-18.5

15-60 70°±2

3,374,155

As an example of applying the oxide coating using the sulfuric acid, the electrolyte was as follows:

Concentration of sulfuric acid, percent____

Current density, amps./sq.ft.____________

Time of treatment, minutes_____________

Temperature of solution, ° F.___________

Procedure to make the oxide coating resistant to corrosive agents

The aluminum oxide coating as produced by the above electrolytic process with or without being sealed in boiling water is not resistant to weak caustic solutions such as are used in detergents. This makes it impossible to use this coating on equipment subjected to many detergents such as cooking utensils, clinical ware, automobile trim and other applications unless special precautions are taken in the cleaning operations and selection of detergent. The oxide coating is also subject to hydration when exposed to water, especially at elevated temperatures, which again limits its use on aluminum articles. Such aluminum oxide coatings are also attacked by salt solutions of rather low concentration which prevents its use in many applications where it would come m contact with these solutions. Likewise forming a coating chemically on aluminum in accordance with the teachings of the prior art is subject ²⁵to the same disadvantages.

In order to provide the above oxide coated aluminum with a modified coating of this invention it was treated as follows:

Procedure A.—Activate the coating

The oxide coating obtained by the anodic process is thoroughly rinsed in water and then activated by heating it in a solution of an inorganic base, for example, 0.2-0.55 gram sodium hydroxide or potassium hydroxide, per liter of water at boiling temperature (212° F.) for 5 to 15 minutes. In order to obtain best results there should be a constant stirring of the solution either from the heat applied or by means of mechanical or air agitation.

That is, the aluminum oxide coating is immersed in a solution of an inorganic base of about .15-1.1 grams solute per liter of water; for example, about .15-1.1 gm./liter of NaOH or KOH (preferably about .2-.55 gm./liter); or about .3-.6 gm./liter of Na₃PO₄ (preferably closer to .3 gm./liter); or about .26 gm./liter of Na₂CO₃ or about .4 gm./liter of NH₄CO₃. Sodium hydroxide and potassium hydroxide are preferred to the other bases mentioned. That is the activation treatment can be carried out at about 5—30 minutes at a temperature range of about room temperature to 250° F. with a base of the general type indicated of about .015-.11% concentration. However as indicated before, the activation step is to be carried out so that it does not too severely attack the coating, and in particular, leaves a partial aluminum oxide coating covering the entire exposed surface.

Preferred procedure:

(1) Rinse the oxide from the anodizing process in water.

(2) Expose to a solution of about 0.2-.55 gram sodium hydroxide or potassium hydroxide per liter (.02-.055%) of water at boiling temperature for 5-15 minutes.

(3) Rinse with water.

Procedure B.—Expose to a solution of organic compounds of the iron group metals

After operation A, the thus coated sheet is exposed to 0.5 to 2% solutions (desirably 5-10 grams/liter) or organic compounds of the iron group metals such as acetates, citrates, oxalates, tartrates and others which hydrolyze on heating to form oxides such as chromium, nickel, iron, cobalt, and zinc. The specimen from Procedure A is exposed to the solution mentioned of this procedure at about 120° F. to 250° F. for a period of 75 adhering film.

to 30 minutes (desirably 140°-180° F.) and then rinsed in water.

Alternately, the solution is desirably .5-15.5 cc. concentrated ammonium hydroxide or 9—10 grams of ammonium citrate per liter of water at about room temperature to 250° F. for a period of 10 to 30 minutes and then rinsed in water.

It is preferred that a mixture of about 5 grams of nickel acetate and 5 grams of ferric ammonium citrate dissolved in one liter of distilled water or .5—5 cc. of concentrated ammonium hydroxide per liter or about 10 grams ammonium citrate, to be used to give the most consistent results. If the solutions of nickel acetate or ferric ammonium citrate are used separately, a concentration of about 10 grams per liter is used. It is also preferable that the solution is at most only slightly acid or one which can be made nearly neutral by adding, for example, NaOH without precipitating the metallic ions. The more acid solutions do not produce as good results.

Preferred procedure:

(la) Expose to a solution of about equal parts by weight of nickel acetate (5 grams per liter) and ferric ammonium citrate (5 grams per liter) at 160° F.±5° F. for a period of 15 minutes. (Note: either of these salts by itself will produce good results but the mixture gives more consistently reproduceable results and increased corrosion resistance); or (lb) Expose to a solution of ammonium hydroxide (.5-5 cc. concentrated ammonium hydroxide per liter) at about 200° F. for a period of 15-20 minutes; or (1c) Expose to a solution of ammonium citrate (9-10 grams per liter) at about 200° for 15 minutes.

Piocedure C. Expose to a solution of alkali or alkaline earth organic compounds

The coated sheet from Procedure B is exposed to a .5 to 2% solution (desirability 5-10 grams per liter of distilled water) of organic compounds of potassium, sodium magnesium, calcium, barium, or strontium, such as acetates, citrates, oxalates, tartrates and others at about 120°250° F. for about 15-45 minutes and desirably at 160°212° F. However a near boiling temperature is preferred. _ It has been found that about 10 grams per liter solution of magnesium acetate or potassium acetate at about 212° gives very good results. The coated sheet of Procedure B is preferably exposed to about 8 to 20 grams per liter solution of magnesium or potassium acetate at about 212° F. for 30±10 minutes and rinsed in water.

Preferred procedure:

(1) Expose to 8-10 grams per liter solution of magnesium acetate or potassium acetate at about 212 for about 20-40 minutes.

(2) Rinse in water.

F.

Procedure D.—Reacting the treated coating of Step with silicate

The coated sheet from Procedure C is next exposed an aqueous solution of sodium or potassium silicate (14 , 60 cc. to 112 cc. liter of water) for a period of 15 minutes to an hour at about 200° to 250° F. It is preferred that Kassil #1 silicate made and sold by Philadelphia Quartz Co. be used. The solution should be kept at about 212° F. and agitated either by heat or other methods. Silicates 65 having a percent Na₂0:percent Si0₂ ratio of about 1:3.20 to 1:3.75 or a percent K₂0:percent Si0₃ of about 1:2.50; the potassium silicate solution being preferred to the sodium silicates.

Preferred procedure:

(1) The coated sheet from Procedure C is exposed to a solution consisting of 28 to 56 cc. of potassium silicate (Kassil #1) in a liter of water at about 212° F. for a period of 30 minutes.

(2) Rinse in water, dry and buff to remove any loosely to

3,374,155 and D of Part I for producing the modified coatings obtained following the anodizing process of Part I. The alternate methods of Parts II, III and IV given do not give as good results as in the case of the anodic coatings method of Part I.

The sheet of drawings summarizes the various steps of this invention.

General comments relative the examples

All of the specimens of the examples were made oi aluminum or an alloy thereof, the type of alloy being indicated for a given specimen when a record was kept of the alloy. Although not specifically indicated for each of the specimens that were subjected to an anodic treatment, each of such specimens was cleaned in a manner set forth under the heading “Finishing and Treatment Prior to the Application of the Oxide Coating” or as set forth in the various examples. Further even though not specifically indicated, after the anodic treatment,, if used, the respective specimens were thoroughly rinsed in water. Likewise after each treatment in accordance with Procedure A, Procedure B, Procedure C and Procedure D respectively, where used, each of the specimens was thoroughly rinsed in water.

Unless otherwise noted, the effectiveness of the successive treatments in the various solutions indicated was determined by immersing the treated specimen in a 1% NaOH solution at room temperature (corrosion test). The results of the corrosion test are based on visual observations by the naked eye. Other than for the indication of “no attack” and “no noticeable attack,” no observations were made other than for the period of elapsed time indicated.

In some cases two compounds were mixed to form a binary solution. For example with reference to Specimen 26 /Table 4) under Procedure B, “NiAc₃+FeNH₄C (4.9 gms. each/liter)” indicates that a quantity of nickel acetate and a quantity of ferric ammonium citrate were each added to water to give the concentration per liter 40 referred to; i.e. if one liter of water was used, 4.9 grams of nickel acetate and 4.9 grams of ferric ammonium citrate were added to one liter of water.

A resume of the test results for the specimens of all examples which were not subjected to any of the treat10

Part II.—Alternate method (A) of obtaining effect of iron group metal oxides in the aluminum oxide coating

Some of the heavy metals such as vanadium, molybdenum, tungsten, columbium, chromium and manganese are amphoteric which makes it possible to add these oxides to the aluminum oxide coating during the anodizing process. For some applications, sufficient resistance to corrosion can be obtained by the method to be described and thus save the cost of Procedure B given in Part I. The results indicate that for maximum corrosion resistance, Procedure B is necessary.

The amphoteric metals mentioned above form vanadates, molybdates, tungstates, columbates, chromates and manganates or permanganates. By adding either the sodium salt or the acid (1—5%) of these amphoteric metals to 15-20% sulfuric acid, the negative ion containing the metal will go to the anode with the sulfate ion during the anodizing operation and deposit the metallic oxide in the aluminum oxide coating.

The procedure for making the coating corrosion resistant would be the same as that previously disclosed under Part I. However for some applications the addition of the amphoteric compounds to the sulfuric acid would replace Procedure B.

Part III.—Alternate method of introducing oxide in the aluminum oxide coating

Many metals including the heavy metals, the alkali earth metals, magnesium and zinc can be introduced into aluminum as an alloying constituent. For example, by adding these elements to the aluminum, as an alloying constituent and choosing the proper anodizing conditions of acid composition and temperature, the desired oxides can be incorporated in the aluminum oxide during the anoidzing process. Typical alloys would be 1-2% magnesium and .5 to 1% of any one of the following: chromium, molybdenum, vanadium, iron, nickel, manganese, cobalt and columbium. Also more than one heavy metal could be added to the alloy to obtain the desired result. There are limits as to the amount of metal that can be added depending on the solubility, the effect on the properties of aluminum as well as the finish on the final product. For some applications sufficient rescribed in Part I (with or without Procedure B) with the indicated modification and thus save the cost of Procedure B given in Part I. Results indicate that for maximum corrosion resistance Procedure B is necessary.

The alkali earth metals are very insoluble in aluminum 50 and cause difficulties in the fabrication of the aluminum so that this addition of these to aluminum is not recommended.

Magnesium and zinc are very soluble and there are many alloys of aluminum that contain these two metals. 55 The results thus far indicate that with the present alloys there is insufficient oxide formed to give maximum corrosion resistance and therefore it is not expected that the addition of these to the aluminum will replace Procedure C.

Part IV.—Oxide coating by chemical methods

Aluminum oxide can be formed as a protective coating by chemical methods. Essentially the solution used consists of a base such as sodium carbonate and an.oxidizing agent such as potassium dichromate. The coating is ap- 65 plied by immersing the aluminum in this solution at a temperature of 140 to 150° F. for various periods of time. Two of these conventional coatings used to considerable extent in industry are designated by the trade ____________________ names Alrok and Iridite. These coatings are soft as com- 70 NaOH (.32gms./liter) pared with those obtained by the anodic process and are not as resistant to corrosive mediums.

The corrosion resistance of these coatings (for example, Alrok and Iridite) can however be increased considerably

L11C 11110.1 piuuuuu * vi omaxxv ---------- -- ----- _r - . - j . — sistance to corrosion can be obtained by the method de- 45 ment steps of Procedures A through D is found in ExEXAMPLE 1

In order to determine the effect of pretreatment on specimens before artificially producing an aluminum oxide coating on the specimens, various specimens were pretreated as indicated in Table 1.

table 1 ample 3.

<td> Specimen</td><td> Alloy</td><td> Pretreatment</td>

<td> 1, 2___________</td><td> 5457</td><td> Degreased and then a caustic etch.</td>

<td> 3_____________</td><td> 3003</td><td> Do.</td>

<td> 4, 5___________</td><td> 5052</td><td> Do.</td>

<td> 6.____________</td><td> 5457</td><td> Degreased and then a bright dip.</td>

<td> 7_____________</td><td> 3003</td><td> Do.</td>

<td> 8_____________</td><td> 5052</td><td> Do.</td>

<td> &lt;</td><td> 5457</td><td> Degrease, next a bright dip, and then a caustic etch.</td>

<td> 10____________</td><td> 3003</td><td> Do.</td>

<td> 11____________</td><td> 5052</td><td> Do.</td>

Each of Specimens 1-11 inclusive were thereafter subjected to a 45-minute anodic sulfuric acid electrolyte treatment and then successively subjected to a treatment in each of the solutions below in the order given as follows:

Solution (b) NiAcs+’FeNSjC (4.9 gms eachjiter)..

(c) MgAcs (9.8 gms./liter)___________________ (d) Kassil #1 (66 ec./liter)-------------------

Time Temperature (min.)

Boiling. 160-170° F.

Boiling.

Do.

auu ναι._________ ----------------- To be mentioned is that after the anodic treatment by the same procedure outlined under Procedures A, B, C 75 and after the treatment in each of the above solutions

3,374,155 each specimen was rinsed with water. The specimens were then subjected to the corrosion test referred to heretofore. The results are given in Table 2 below.

A and B; Table 5 the treatment of Procedures C and D; and Table 6 the results of the NaOH corrosion test.

TABLE 2

Specimen Elapsed Results of Corrosion Test time (hrs.)

TABLE 3

Treatment

1.

2.

3.

4.

5.

6.

7_______

8_______

9, 10, 11.

Slight edge attack and in scratch, no other attack.

Attack on one side, checks with 1, 5.

Slight attack in scratches, 2 small pits each side no other attack.

A few small pits one side, 2 pits on other.

Slight attack one scratch, no other attack.

One side no stains, other large area of stains no attack.

No attack one side without stains, severe pitting and corrosion in stained areas.

Stained areas, but no attack.

4 small pits one side, 18 small pits other, some of these stained areas.

Stained, but not attacked.

Medium pitting on one side, slight pitting on other, severe attack in stained areas.

No attack, but numerous stains.

Severe small pitting.

Specimen Ally

<td> 12-15_______</td><td> 3003</td>

<td> 16..........</td><td> 3003</td>

<td> 17__________</td><td> 3003</td>

<td> 18__________</td><td> 5457</td>

<td> 19,20________</td><td> 5457</td>

<td> 21.........</td><td> 3003</td>

<td> 22........</td><td> 5052</td>

<td> 23..........</td><td> 3003</td>

<td> 24...........</td><td> 5052</td>

<td> 25.......</td><td></td>

<td> 26___________</td><td> 3003</td>

<td> 400..........</td><td> 1100</td>

<td> 401,402______</td><td> 3003</td>

Only chromic acid electrolyte for 40 mln.

Degrease, caustic etch, bright dip, 1 hr. sulfuric acid electrolyte.

Degrease, caustic etch, bright dip, 15 min. sulfuric acid electrolyte.

Degrease, 30 second caustic etch, water rinse, 30 min. sulfuric acid electrolyte followed by 5 min. chromic acid electrolyte.

Degrease, 30 second caustic etch, water rinse 30 min. sulfuric acid electrolyte.

Same as specimen 18.

Same as specimen 19.

Do.

Same as specimen 19 other than foaming agent was added to electrolyte.

Hard coat.

Degrease, caustic etch and 45 min. sulfuric acid electrolyte.

min. caustic etch, 2 min. in H₂SO₍ etching solution and 45 min. sulfuric acid electrolyte.

Iridite 3 min., dilute caustic etch 3 min., and 45 min. sulfuric acid electrolyte.

The modified coated Specimens 6, 7 and 8 appeared ²⁵stained in areas, however this was undoubtedly caused by the bright dip as staining was observed on the specimens after the bright dip treatment. The caustic etch did not remove these stains entirely. From Specimens 1-11 it can be seen that using only the caustic etch instead of ³⁰the bright dip or in combination therewith better results were obtained. However good results can be obtained in using a bright dip during pretreatment as shown by Specimens 6, 7 and 8. Further as indicated by Specimens 16 and 17 of Example 2 very good results can be obtained ³⁵when a bright dip is used in the pretreatment of specimens.

TABLE 6

Specimen

Elapsed Time (hrs.)

Corrosion Results

12,14,15,16_____

13,17___________

18,21,25._______

19,20,22________

23______________

24______________

EXAMPLE 2

A further illustration of using various pretreatments and types of aluminum oxide coatings are shown by the specimens set forth in this example, Table 3 setting further the pretreatment steps, if any, and the type of alu- ,_rminum oxide coating; Table 4 the treatment of Procedures .

No attack.

Do.

No noticeable attack.

No attack.

Slight pitting.

No attack.

Considerable pitting.

No attack.

Attack in small scratches on one side, pit on other.

No attack.

Do.

Do.

9¼ Small pits at bottom edge one side, 2 small pits other.

Same as 9½ hrs.

14½ No attack.

Start of attack in large. area one side, severe attack large area on other.

TABLE 4

<td> Specimen------------------</td><td> Procedure A</td><td></td><td> Procedure B</td>

<td> Solution</td><td> Time</td><td> Temp.</td><td> Solution</td>

<td rowspan="2"> 12-17----------NaOH (.30 gms./l.) 18, 21, 25______NaOH (.29 gms./l.) 19, 20, 22, 23... NaOH (.29 gms-./l.) 24-------------NaOH (.29 gms./l.).. 26-------------NaOH (.32 gms./l.).. 400..... NaOH (see Note 1)_. 401..... NaOH (.30 gms./l.).. 402.-----------NaOH (.30 gms./l.)..</td><td> --------10 min...... ------10 min______ ...... lOmin......</td><td> . 212° F_________ . Boil........... ......do_________</td><td> NiAc3+*FeNH₄C (4.3.gms. each/liter).......... NiAc3-f-*FeNH₄C (4.6 gms. each/liter). _____do___________</td>

<td> ------10 min...... ...... lOmin...... ------15 min______ ------15 min______ ------15 min......</td><td> .....do......... ______do......... _____.do_________ ------do_________ -----do.........</td><td> UrAcrPleN.EuC (4.6 gms. each/liter).......... NiAcs-HFeNHjC (4.9 gms. each/liter)______ NH₄0H (see Note 2)....._ *NHiC (9 gms./liter)____________________ *NH₄C (9 gms./liter).............._____</td>

Time Temp.

min______ 120-140° F.

min......, 148° F.

min______ 178-180° F.

min...... 175° F.

min______ 160-170° F.

min______ 200-212° F.

min______ 200-212° F.

min 200-212° F.

Specimen

Solution

TABLE 5

Procedure C Procedure D

Time Temp.

Solution

12-17________

18, 21, 25..,.

19, 20, 22, 23.

24...........

26...........

400..........

401..........

402..........

MgAcz (8.9 gms./l.)........

MgAcj (9.4 gms./l.)........

None.......________________

MgAc2 (9.4 gms./l.)________

MgAca (9.8 gms./l.)........

None.............._.........

_____do......................

KAc (9.8 gms/1.)..........

min______212° F.........

30min...... Boil............

min______Boil...........

30min...... Boil............

Liq. G.T.W. (28 cc./liter). Liq. Na₂SiO₄ (66 cc./liter) Kassil #1 (56 cc./liter).....

Kassil #1 (28 cc./liter)......

....do.....................

....do................

-----.....................—.....,αο.

mm 200-212° F..........do.

Note 1.-NaOH of a concentration to require 2.1 cc. of 0.1 NHC1 Note 2.-NH₄0H of a concentration to require 4.80 cc. of 0.1 HC1 to neutralize a 25 cc. sample of solution, to neutralize a 5 cc. sample of solution.

Time Temp.

hr.........212° F.

min...... 212° F.

min______Boil.

min...... Boil.

min....... Boil.

min...... 200-212° F.

min...... 200-212° F.

min 200-212° F.

3,374,155

With reference to the specimens included in Tables 4-6, attention is also directed to the specimens of other examples where various other pretreatments also gave very good results as follows.

EXAMPLE 3

Interspersed with other specimens that were treated in accordance with this invention were various specimens that were not so treated. For these various specimens the 5 pretreatment, if any, is set forth in Table 7 while any further treatment and the test results are set forth in Table 8.

TABLE 7

Specimen Alloy Pretreatment

Artificial Oxide Coating

27_.

28-.

2930_.

3132217.

221.

222.

637.

640.

5457

3003

3003 5457

5052

3003

3003

3003

1100

1100 hr. sulfuric acid electrolyte.

min. sulfuric acid electrolyte.

Only 40 min. chromic acid electrolyte.

............................... Only Iridite dip.

Degrease’’ 30 sec. caustic etch, water 30 minutes sulfuric acid electrolyte, rinse.

Degrease, 1 min. caustic etch, 2 min. bright dip.

See Example 20.........................See Example 20.

„.do___________________________ Do.

do________________________ Do.

1% caustic etch..........................45 min. sulfuric acid electrolyte.

_____do_________________- Do.

Degrease, bright dip----Caustic etch, bright dip

Do.

TABLE 8

Specimen.

Further Treatment

Elapsed Time

Corrosion Test Results

27___________30 min. boiling water seal.. _ 15 min-----1¼ hrs______

28...........Boiling water seal........... 1 min.------2 min......29 ...........--do----------------------2 min------10 min......

30___________None_________________________-............

31..,.........20 min. boiling water seal—. 2½ min----32________________do_______________________3 min_______

217__________15 min. boiling water seal... 2 min.......

221...............do.............-.........16 hrs.......

hrs.......

Noticeable attack. All coating dissolved. Oxide coating partially remove. Very severe attack.

Noticeable attack.

Very severe attack.

Coating removed in minutes.

Very severe attack.

Severe attack.

Do.

Noticeable attack.¹

Considerable attack, some coating still on specimen.¹

2½ min_____Coating dissolved.²

1¼ min_____Very severe attack.

min_______ Do.

222.............-do.......................

637........ Boiling water seal,..........

640....... do.......................

Specimens

Example

14 15

8

21 21 21

21 ¹ Oxalie corrosion test (room temperature).

Oxalic corrosion test (boiling).

As will become more apparent hereinafter, treating specimens in accordance with this invention substantially enhances the corrosion resistance of aluminum over and above that obtained in treating specimens in accordance with this Example.

Elapsed Time Showing No Attack (hrs.)

202, 203_____

189, 190, 191. 193, 194_____

63__________

100_________

422-426_____

427_________

429_________

430_________

431_________

432_________ ____

From the results shown in Examples 2 and 3, it is to be noted that a very wide variance of pretreatment is possible without having an adverse effect on the final product, it being noted all the specimens of Example 2 (except 401, 402), including those subjected to a bright dip during the pretreatment, withstood the corrosion test for at least 20 hours with no noticeable attack. These results are to be contrasted with those set forth in Example 3.

EXAMPLE 4

A series of specimens were provided with an artificial oxide coating by various electrochemical and chemical procedures and then subjected to various treatments of one or more of Procedures A-D. The type of aluminum oxide coating is set forth in Table 9 for some of these specimens while the treatment intermediate the oxide coating of Table 9 and the corrosion test is set forth in Tables 10 and 11. With reference to Specimens 408, 409 they were given a Iridite coating by exposing to the solution for five minutes and then rinsed in water.

TABLE 9

<td> Specimen</td><td> Alloy</td><td> Oxide Coating</td><td> Elasped Time (hrs.)</td><td> Corrosion Test Result</td>

<td> 33___________</td><td> 3003</td><td> Iridite dip____</td><td> 19</td><td> Considerable pitting but coating intact.</td>

<td> 34___________</td><td> 3003</td><td> Alrok #4______</td><td> 4 30</td><td> No attack. Very severe attack in center areas.</td>

<td> 35___________</td><td> 3003</td><td> Hard coat_____</td><td> 15 20</td><td> No noticeable attack. Severe pitting.</td>

<td> 36___________</td><td> 5052</td><td> _____do________</td><td> 15 20</td><td> N o noticeable attack. Slight pitting.</td>

<td> 37___________</td><td> 5457</td><td> _____do________</td><td> 8 15 20</td><td> Only attack on scratches. Do. Very slight pitting.</td>

<td> 38___________</td><td> 7075</td><td> _____do________</td><td> 15 20</td><td> No noticeable attack. Slight pitting one side, none on other.</td>

<td> 39___________</td><td></td><td> . do________</td><td> 20</td><td> Medium amount of medium size pits.</td>

<td> 405__________</td><td> 7075</td><td> _____do________</td><td> 4¼ 6 7</td><td> No attack. No attack one side, series of pits in a scratch on other. Do.</td>

<td> 406__________</td><td> 5457</td><td> _____do________</td><td> 4¼ 6 7</td><td> No attack. 2 pits in scratches one side, a series of pits in line on other. 4 pits in scratches one side, a series of pits in line on other.</td>

<td> 407__________</td><td> 3003</td><td> Alrok #4______</td><td> 7</td><td> No attack.</td>

<td> 408__________</td><td> 3003</td><td> Iridite dip_____</td><td> 5¼ 6</td><td> Do. Slight attack.</td>

<td> 409__________</td><td> 3003</td><td> _____do_________</td><td></td><td> No attack.</td>

3,374,155

TABLE 10

Specimen_____________________ Procedure A

33-------------NaOH (.30gms./l.),....

34------------. NaOH (.32gms./l.)....

35-------------NaOH (.29 gms./l.)___

36-------------NaOH (.29mgs./l.)....

37............. NaOH (.29 gms./l.)....

38------------- NaOH (.29 gms./I.)....

39------------NaOH (.29 gms./l.)____

405—.......... NaOH (.32gms./l.)...

406............ NaOH (.32 gms./l.)....

407............NaOH (.32gms./l.)....

408,409—.....(NaOH-,32 gms./l. plus

NH4OH-7.5 cc. cone./ liter).

Procedure B min..

min..

min_.

min..

min..

min..

min...

min..

min._ min_.

min_.

£¹² F......... NiAc3-H*FeNHjC (4.3 gms. each/liter).

Boil......-----NiAcs-pFeNHaC (4.9 gms. each/liter)

-----do........None_______

-----do.............do___________ 2”-”-?

.....do.............do.....................

-----do.............do..................

4...d0;-----... NiAcj+*FeNHiC (4.8 gms. each/liter)

....do--------NH4OH (7.9 cc. conc./liter)____________

....do.-------NH4OH (7.9 cc. conc./liter)____________

....do........NH4OH (7.9cc. conc./liter).....___

...—do...-----*NHiC (9 gms.Alter)...........

min.

min.

120-145° F.

160-170° F.

- 15 mln______150° F.

— 15 min______ 200-212°F.

... 15 mln______ 200-212°F.

... 15 mln______ 200-212°F.

... 30 min______ 200-212°F.

TABLE 11

Specimen

33...........

34..,........

35...........

36...........

37...........

38...........

39___________

405...-......

406________

407.........

408, 409......

Procedure C

<td> MgAc₂ (8.9 gms./l.)_...</td><td> . 30 min...</td><td> ... 212° F.</td>

<td> MgAc⁸ (9.8 gms./l.)._..</td><td> .... 30min...</td><td> — Boil..</td>

<td> MgAca (9.4 gms./l.)_____</td><td> —30min....</td><td> ... 212° F.</td>

<td> MgAcj (9.4 gms./l.) ...</td><td> —30 min.....</td><td> ... 212° F.</td>

<td> MgAc₂ (9.4 gms.A·)_____</td><td> —30 min....</td><td> ... 212° F.</td>

<td> MgAc₂ (9.4 gms.A.)_____</td><td> .... 30min....</td><td> ... 212° F</td>

<td> MgAci (9.4 gms./l.)_____ None_______</td><td> .... 30 min....</td><td> ... Boil...</td>

...do.. ... do__ ..do...

Procedure D

Kassil (59 cc./liter) Na₂SiOs (56 cc./liter) _ Na₂SiC&gt;3 (56 cc./liter). Na₂SiOa (56 cc./liter). NaaSiOa (56cc./liter). Na₂SiOs (56 cc./liter).

Ni₂SiO (56 cc./liter) Kassil #1 (27 cc./liter) .....do............... .....do............... _____do....._____.....

... 1 hr_________212° F.

... 30 min______Boil.

.. 30 min______212° F.

.. 30 min______212° F.

... 30 min______212° F.

... 30 min______212° F.

.. 30 min______212° F.

... 30 miu______ 200-212°F

.. 30 mln...... 200-212°F.

... 30mln..____ 200-212°F

... 30 min 200-212 F.

The specimens of Tables 12—14 illustrate other variations in the method of forming an aluminum oxide coating on aluminum articles prior to subsequent treatment.

next given the treatment indicated under “Further Treatment,” rinsed and treated to the solutions of Tables 13 and 14 before the corrosion test.

TABLE 12

<td> Specimen</td><td> Alloy</td><td> H₂SO₄Electrolyte</td><td> Further Treatment</td><td> Elapsed Time (hrs.)</td>

<td> 40____________</td><td></td><td> .. 1 hr..........</td><td> _ Heated at 375° F. for 1 hour___</td><td> 12</td>

<td> 41___________</td><td> 3003</td><td> 30 min_______</td><td> . Foaming agent added_________</td><td> 15 27</td>

<td> 42___________</td><td> 5457</td><td> 30 mln.......</td><td> _ 3 min. chromic acid electrolyte.</td><td> 17</td>

<td></td><td></td><td></td><td></td><td> 24</td>

<td> 43__r_________</td><td> 3003</td><td> 30 min_______</td><td> ______do________</td><td></td>

<td> 44___________</td><td> 5052</td><td> 30 min_______</td><td> ______do__________</td><td></td>

<td> 45-........</td><td> 5052</td><td> 30 min_______</td><td> ......do......... .</td><td></td>

<td> 46___________</td><td> 5457</td><td> 30 min.______</td><td> ______do________________________</td><td> 24</td>

<td> 47___________</td><td> 5457</td><td> 30 min.______</td><td> ------do__________</td><td> 24</td>

<td> 48___________ 49...........</td><td> 3003 3003</td><td> 45 min_______ 45 min_______</td><td> . 5 min. chromic acid electrolyte. ______do.. .</td><td> 20</td>

<td> 50,51........</td><td> 5457</td><td> 30 min.......</td><td> ......do_________________.......</td><td> 15</td>

<td> 52_________</td><td> 5052</td><td> 30 min_______</td><td> ______do_______</td><td> 20</td>

<td> 410..........</td><td> 3003</td><td> None.........</td><td> . 40 min. chromic acid electro-</td><td> 6</td>

<td></td><td></td><td></td><td> lyte.</td><td></td>

<td> 411__________</td><td> 3003</td><td> -----do_______</td><td> ------do_____________________</td><td> 10 10</td>

<td></td><td></td><td></td><td></td><td> 13</td>

<td> 412__________</td><td> 5005</td><td> _____do_______</td><td> ------do__________________</td><td> 16</td>

<td></td><td></td><td></td><td></td><td> 20</td>

Corrosion Test

No attack.

Considerable shallow pitting on both sides. Few pits one side, attack In scratches on other.

No attack.

Both sides numerous small pits and large area of attack like fingerprint.

Medium small pits both sides, 2 large areas of attack like fingerprints.

Severe attack that appeared like fingerprints, other, a few small pits and attack In scratches.

Few small pits one side, 3 pits other.

Numerous small pits both sides, severe attack on bottom.

Numerous small pits both sides.

Few small pits both sides.

No attack one side, five small pits on other.

No noticeable attack.

Numerous small pits.

Very slight pitting.

No attack.

Severe pitting.

No attack.

Medium general pitting one side, several general pitting other.

No attack.

Considerable pitting.

Each of Specimens 40-52 of Tables 12-14 were cleaned by a pretreatment, then subjected to a sulfuric acid electrolyte for the time indicated in Table 12 and subsequently treated to solutions indicated in Tables 13 and 14 before the corrosion test; while Specimens 410, 411 and 412 were degreased, subjected to a dilute caustic etch,

With reference to Specimens 40, after the anodic treatment it was heated at 375° F. before being treated to the Procedure A solution; to Specimen 41 the foaming agent was added to the electrolyte solution; and for the other specimens, the chromic acid electrolyte treatment followed the sulfuric acid electrolyte treatment but was before the treatments set forth in Tables 13 and 14

TABLE

Specimen

40...........

41___________

42...........

43............

44...........

45.........

46____________

47...........

48___________

49____________

50_____________

51, 52________

410____________

411..........

412___________

Procedure A

NaOH (.15 gms./l.).

NaOH (.29 gms./l.).

NaOH (.29 gms./l.) NaOH (.29 gms./l.).

NaOH (.29 gms./l ). NaOH ¢.29 gms./l.). NaOH ¢.29 gms./l.). NaOH (.29 gms /1.). NaOH (.32 gms./l). NaOH (.32 gms./l.).

NaOH (.29 gms./l.).

NaOH (.29 gms.fi.) NaOH (.3:gms./l.)_. NaOH (.3 gms./l.)..

NaOH (.3 gms./l.)..

5min___ 10 min.. 10 min.. 10 min.. 10 min... 10 min... 10 min-. 10 min.. 10 min._ 10 min_. 10 min.. lOmin.. 20 min.. 15 min.. 15 min. _

Procedure B

120-140 F-----NiAcs+’FeNHiO (4.6 gms. each/liter), ^Boli----------- CrAoi+’FeNHjG (4.6 gms. each/liter).

-----5°---------NiAc₃+*FeNHiC (4.6 gms. each/liter).

-----do--------------do____________________”

-----do--------------do___________________

-----do--------------do_______... .LiLLl” __' “

-----do--------------do_____________________

-----do---------NiAc₃+*FeNHjC (4.9 gms. each/liter)'

-----uo---------------do_______________

....do---------None____________

---do---------NlAc₃+*FeNHiC (4.6 gms. each/liter).

.-...do.--------------do...

—.do--------- *FeNH₄C min------- 120-140° F.

min______175° F.

min______175° F.

min.______175° F.

min______175° F.

min______175° F.

min______175° F.

175° F.

160° F.

160° F.

146-148° F.

min.

min.

min.

200-212° F.

3,374,155

TABLE 14

Specimen Procedure C

Procedure D

4fl ___________MgAc: (8.9 gms./l.)

41_MgAca (9.4 gms./l.) _

42____________MgAca (9.4 gms./l.) _

43_MgAcj (9.4gms./l.).

44_Mg Acs (9.4 gms./l.).

_________MgAcz (9.4 gms./l.).

46_________MgAcj (9.4 gms./l.).

47________MgAcz (9.4 gms./l.)-

48_Mg Acs (9.8 gms./l.).

_______MgAci (9.8 gms./l.).

50_, 51, 52______MgAcj (9.4 gms./l.).

410____________None---------—

411 __________KA. (9.8 gms./l.) —

412____________KA o (9.8 gms./l.) — mln______212° F----30 min------Boil------30 min___________do----30 min-----------do----30 min-----------do----30 mln-----------do----30 min-----------do----30 mln----------30 min______ 200-212° F.

min______ 200-212° F.

min______212° F—.

Lin. G.T.W. (28 cc./Uter)... Kassil #1 (28 cc./liter)-----_____do_____________________ _____do_____________-.......

_____do_____________________ _____do_____________________ _____do_____________________ _____do_____________________ _____do_____________________

Liq. G.T.W. (56 cc./liter). Kassil #1 (27 cc./liter)-----30 min______ 200-212° F----------do----------------------------30 min______ 200-212° F----------do----------------------------... 1 hr.........

min-----30 min-----.,. 30 min-----... 30 min______

... 30 min______

.... 30 min-----.... 30 min-----.... 30 min-----.... 30 min......

.... 30 min______

.... 30 min______

.... 30 min_____.... 30 min-----212° F.

Boil.

Do.

Do.

Do. Do. Do.

Do.

200-212° F.

200-212° F.

212° F.

200-212° F.

200-212° F.

200-212° F.

With reference to the specimens of Tables 12-14, attention is also directed to specimens of other examples as follows:

Specimen: Example

12-15, 18, 21, 24, 25

29, 30

122, 124 _________________________________

104, 107, 108

166-169, 172

GENERAL COMMENTS (1) Contrasting Specimens 33, 34 with the specimens of Table 3 and 30 of Example 3, it is to be noted that the corrosion resistance of a chemically produced aluminum oxide coating is substantially increased by providing the modified oxide coating of this invention.

(2) As indicated by Specimens 153-156 (Example 11), 50 and 51, and Specimens 18, 21, 25 of Example 2, and 39 (Example 4), the regular sulfuric acid anodic treatment, the regular sulfuric acid anodic treatment followed by a chromic acid anodic treatment and the “hard coat” sulfuric acid treatment, each followed by steps that include an activation step and exposing the specimens to the silicate solution give good results, i.e. substantially increase the corrosive resistance above that of the untreated specimens. Also the chromium oxide in the modi- ment followed by the noted steps which included the NiA.₃, FeNH₄ citrate treatment. The manganese did not give the aforementioned effect (see Specimen 35) while the 5457 and 7075 alloys did.

EXAMPLE 5 ²⁰ In order to ascertain which of Procedures A, B, C and D were necessary in order to substantially enhance the corrosion resistance, the series of specimens referred to in Table 15 were tested.

All the specimens of Table 15 were subjected to treatment in accordance with the following steps other than for the steps indicated as omitted in Table 15. The specimens were treated as follows (note adjustment of alkalinity of Example 6):

(a) Flash sulfuric acid electrolyte treatment of one minute.

(b) caustic etch—20 seconds.

(e) NaOH (.32 gm./liter) 10 minutes at boiling.

(d) Thoroughly rinse with water.

(e) NaOH (.32 gms./liter) 10 minutes at boiling.

(f) NiAc₃+*FeNH₄C (4.9 gms. each/liter) 30 minutes, 160° F.±5° F. .

(g) Mg. acetate (9.8 gms./liter) 30 minutes, 200 F.+, but not boiling.

(h) Kassil #1 (28 cc./liter) 30 minutes, 200° F.+, but not boiling.

TABLE 15

Specimens Alloy

3003

3003

3003

Step NaOH CorOmitted rosion Test, (hrs.)

Remarks ___________ 3003 57___________ 3003

-jne 2» iNoat+uuK.

, ..... 1 Some areas show signs of attack.

.......... 2 Considerable attack as pits and In scratches ₍ _ β Showing slight attack in scratches.

Showing slight attack in scratches and 1 pit.

\ 28 A few small pits.

s..... j All coating dissolved and aluminum

....... attacked.

fied coating produced by chromic acid in the electrolyte or by the chromium in the starting alloy increases the corrosion resistance. However modifying the aluminum oxide by the steps which include the activation step and 60 treatment in a silicate solution substantially increases the corrosion resistance above that obtained by only forming an unmodified oxide coating by utilizing chromic acid in the anodic electrolyte or an aluminum chromium alloy, see Specimens 28, 29, 31, 32 (Example 3) and 217 (Ex- 65 ample 20) where the oxide coating even with a boiling water seal was severely attacked or dissolved in minutes, and Specimens 18, 21 of Example 2 and 39 of Example 4 where the coating remained intact for at least 20 hours.

(3) As indicated by Specimens 50, 51, 52 (Example 70 4) and 35-38 of Example 3, the CR₂O₃ introduced into the regular sulfuric acid anodic treatment, and the chromium in the 5052 alloy produced coatings by omitting the NiAc₃+FeNH₄ citrate, yielded coating as resistant to «corrosion as the pnes with the sulfuric acid anodic treat- 75

As may be noted in particular from Specimens 53—57 (which were treated in freshly made solutions), the treatment in a basic solution of Procedure A and the silicate treatment of Procedure D are the two most necessary steps of this invention in order to enhance the corrosion resistance of an artificially (chemically-or anodically) oxide coated aluminum article. These results cross checked with the treatment of other specimens. Also note Example 3 where specimens were not treated with any of the solutions of Procedures A, B, C and E&gt;.

Also as indicated by the results from Table 15 and otner examples, the presence of alloying elements such as manganese, chromium and magnesium form a modified oxide during the sulfuric acid anodic treatment and act substantially the same as when these same elements, are deposited in the oxide chemically. In many applications, the resistance to corrosion obtained with only forming an oxide coating (electrically or chemically), and then utilizing steps of Procedures A and D would be ample.

3,374,155

Another procedure to obtain a modified oxide coating is to add amphoteric compounds such as manganic, chromic, molybdic, vanadic and permagahic acids, etc. to the anodic solution. This would act in a manner similar to that of the preceding paragraph to increase the corrosion resistance after the specimen was activated with sodium hydroxide and then exposing them to the silicate solution within the approximate concentration and temperature ranges disclosed.

A series of specimens Were first degreased, a flash sulfuric acid electrolyte for one minute, caustic etched, a 45-minute sulfuric acid electrolyte, thoroughly rinsed with water and then successively treated to the solutions indicated in Table 16, the solutions being selected from the following:

TABLE 16—Continued

Speci- Procedures men —-----;-Time elapsed Corrosion Test Results (hrs.)

418...... k

419_____k

420.....k c

11¼ 14

7¼

8¼ (a) NaOH (.32, gm./liter)_____.____10 min Rnllinv (b) NaOH (1-2 gms./liter)--KAc (9.8 gms/ 30 mln______ Do.' (c) (d) (6) (f) (g) (h) (i) (1)

») liter). , ‘ ' UV1U1U-.

W-Sgms. each/liter).. 15min..

,ΚθΝΗ’θ (®·⁸ 8™s-/&gt;*ter)---------------30 min..

MgAca (9.8 gms./liter)....._________... 30 min

KAo (9.8 gms./liter)----------....______30 min

Kassil #1 (28 cc./liter)........... 30 min

NaOH (.3 gm./liter)............... ~ 30mn

KAc (9.8 gm./liter)..._________... 30min

NaOH (.3 gm./liter)________________ 20 min

NaOH (.3 gm./liter ............ 15 mn ’

... 160° F. ... 200°-2Ϊ2° F.

Do.

Do. DO. ... Boiling. ... 1β0°-165° F. — Boiling.

Do.

TABLE 16

Spec!- Procedures men — ---_-—

AB C D

65------af g

66__.a g

67-bg .----. a c eg

-..--. a c eg

70-a ------fg

71_a d g

72-a ______eg

73.- b g

Time elapsed Corrosion Test Results (hrs.)

Edge attack increase όη side, medium attack in scratches and severe attack at one side on other.

No attack.

Do.

areas where coating dissolved one side and most of coating dissolved on other.

No attack.

Slight attack in scratches one side, no attack other.

Slight attack in scratches one side, no attack other, plus medium small pits, numerous smaller pits other.

Same as above.

Prior to the pretreatment of specimens of Table 16 it was noticed Specimens 66-68, 70 had visually noticeable metal defects while Specimens 65, 69 and 71, 72. 73 did 25 not.

413_____h ____________ g

414_____h ____________ g

415_____a ______1 g

416_____a c ______g

417......j ----------„ g

No attack.

Only slight edge attack.

No attack.

Only attack on bottom edge.

No attack.

and Pitting on bottom and side edge.

Above somewhat worse, 6 small pits on side.

No attack.

Few very small pits one side, ho attack on other.

Nd attack.

Only slight edge attack.

No attack.

2 small pits.

Only 2 very small pits.

Pits became larger.

Do.

No attack.

........ Attack along scratches and one side, small pit . on both sides.

No attack.

Pitting on bottom and side edge.

Above and 2 pits on one side.

Severe pitting on bottom and side edges, 2 medium large areas and 3 small‘pits on side but . none oh other.

4¼ No attack.

6½ Attack in scratches.

12¼ Very severe attack oh both cfrlOQ

2¼ No attack.

No attack on side, slight attack in scratches on other.

Slight attack in scratches on both sides.

Same.

Severe attack in scratches both sides and edge attack.

2¼ No attack.

5¼ No attack one side, attack in scratches at bottom on other.

Same.

Few small pits both sides, attack in scratches at bottom on other side· 4¼ No attack either side, few pits on edge.

6¼ Same.

No attack.

Only edge attack.

Edge attack one side, slight attack in scratches and at one side on other.

Edge attack brie side, medium attack in scratches arid at one side on other.

Treatment with the basic solution of Procedure A followed by the silicate treatment of Procedure D in some tests give as good results as using the additional treatments of Procedures B and C; however; the results are not as ³⁰ consistent as when at least one of Procedures B and C are used. Further as exemplified by Specimens 67, 73 attempting to combine Procedures A and C does not give as good results as where the. specimens are sepa35 ^rately treated to solutions of Procedures A and C.

Also as may be noted, potassium acetate and magnesium acetates intermediate the, treatments of Procedures A and D give good corrosion resistance and which is somewhat better than where only a ferric ammonium 40 citrate treatment is interjected between Procedures A and D.

EXAMPLE 6 ⁴⁵ Fresh solutions were made up and a titration of a 25 cc. sample of each solution was made to determine the alkalinity before treating Specimens 53-57 as described in Example 5. The initial alkalinity being indicated in ^Table P ^{by tbe am}ount of .5 normal HC1 required to neutralize the respective solution under the heading initial alkalinity,” and after treating these specimens, the amount required to restore the solutions to the original alkalinity under the heading “restore alkalinity.” These specimens were pieces of strip aluminum, the area of each surface exposed to treatment being about 3 by 5 and the area subjected to the corrosion test being about 3 bv 2to2%. ³⁶θ __________ TABLE 17

Solution Initial Alkalinity Restore Alkalinity MS*™-: ^Na0H· cql.ii/ liter).

MgAc_z (9.8 gms,Alter)------.1 co. of A NHC1 fi re of IV NToOTT

Kassil #1 (28 CA/Uter)-------1.1 _cc. of ,_g NHCL.T Left asL^% °^H'

Samples (25 cc.) of solutions Used for treating Speci70 mens 75 and 80-90 of Example 7 plus two others were titrated to neutral to determine the original alkalinity, then the solutions used for treating specimens (area of each specimen being about the same as given above) and again titrated, the alkalinity being expressed in .1 NHC1 75 in Table 18.

3,374,155

TABLE 18

<td> Solution</td><td> Initial Number of Specimens Restore Alkalinity Final Alkalinity Tested Alkalinity</td>

1.85 cc_......- 74,75,86,87............. 6 cc. l%NaOH.........1.9

1.70 cc........ 84,85, 89 and one.....Dilute 1-1 .75

I.75___________ 80, 81, 90 and one.............................................

1.80___________ 82,83...................Dilute 1-1 .9 nH 6 ........8 specimens.............6 cc. l%NaOH pH 6 .lee_____________.do—................ 10cc. of 1% NaOH______.15

12.15 cc_______15 specimens............Left as is--------------------------NaOH_______________Na₂CO₃......-......—.....

NH4CO3................—Na₃POi___________-NiAca+FeNHiC----------MgAc2......................

Kassil·#!

Solutions that had their alkalinity restored as per the column under Table 18 were used for Specimens 76 and 77 (Example 7) and then their alkalinity restored as indicated in Table 19.

TABLE 19

Solution Specimens Restore Alkalinity Final AlTested kalinity

NaOH 76

Na/PO, 77

NiACa+^FeNHjG.... 76,77

MgAcz 76,77

Kassil#! 76,77

2cc. of 1% NaOH_____ 1.95 cc. of !%NaOH--------------6cc. of 1% NaOH_____ .1 ________________________ 13.3

EXAMPLE 7

In order to determine the effectiveness of varying the basic solution of Procedure A, the specimen of this example that appear in Table 20 were all treated as per steps (a), (b), (c) and (d) of Example 5. The “additional steps” referred to in the table below are the same as the steps set forth in Example 5. With reference to the activation step of this example, the treatment was for 10 minutes at boiling.

Specimen 91 was degreased, bright dipped, subjected to a 45-minute sulfuric acid electrolyte and then treated to the solutions as follows:

¹⁵ NaaCOa (.26 gm./liter)_._.__________________5 min------- 120-140°F.

NIAca (5 gms./liter)_________________________15 min------ 120-140°F.

NaaSiOa (liq. G.T.W. 28 cc./llter)....... 1 hour------- 240-212°F.

While Specimen 92 was degreased, bright dipped and subjected to a 40-minute sulfuric acid electrolyte and then ²⁰ treated to solutions as follows:

NaaPO, (.30 gm.fliter)______________________5 min------- 120-140° F.

NiAcj (8.9 gms./liter)_______________________15 min------120° F.

MgAca (9.5 gms./liter)_______________________ 45 min------212° F.

NaaSlOa (liq. G.T.W. 28 ec./liter)___________1 hour....... 212° F.

²⁵ Specimen 93 was treated the same as Specimen 91 other than the Na₂CO₃ and NiAc₃ solutions were each at room temperature. The results of the corrosion tests were as follows:

Specimen 91____3¾ hours______ hours________

Specimen 92.— 10 hours_______ hours_______ _ _ Specimen 93. 2 hours________

3¾ hours______

No attack.

Slight attack.

No attack except where specimen touched testing rack.

More numerous and larger pits than specimen 135 (Example 11), also areas of no attack.

No attack.

Considerable attack.

Also note that KOH can be used, see Example 17.

As may be noted above the NaOH activation step gave the best results with NH₄CO₃ second best; whereas 40 for Specimens 82-85, 88 and 89 it was noted that the respective activating solutions did attack the aluminum

TABLE 20

<td> Specimen</td><td> Alloy</td><td> Activation Step</td><td> Additional Steps</td><td> NaOH Corrosion Test</td><td> Remarks</td>

<td> 74___________</td><td> 3003</td><td> NaOH, .32 gm./l________</td><td> . f, g, h-------</td><td> . 5 hrs........ 16 hrs.......</td><td> Only edge attack. . Only severe edge attack.</td>

<td> 75___________</td><td> 3003</td><td> NaOH, .32 gm./l________</td><td> . h___________</td><td> . 5 hrs........ 16 hrs_______</td><td> . Only edge attack. . Severe edge attack, 13 medium to small pits one side, none other.</td>

<td> 76-.,-_______</td><td> 3003</td><td> NaaPOi, .56 gm./l_______</td><td> . t, g, h-------</td><td> . 1½ hrs______ 4½ hrs......</td><td> No attack. . Severe attack.</td>

<td> 77...........</td><td> 3003</td><td> NaOH, .32 gm./l........</td><td> . t, g, h-------</td><td> . 4½ hrs______</td><td> . No attack.</td>

<td> 78...........</td><td> 3003</td><td> NajCOs, .25 gm./l.......</td><td> . f, g, h-------</td><td> . 2 hrs._...... 3 hrs........ 5 hrs........ 7 hrs________</td><td> Do. . Brown spots noticeable. . Pitting started in brown spots. . Considerable pitting in brown spots.</td>

<td> 79___________</td><td> 3003</td><td> NaOH, .32 gm./l_______</td><td> . f, g, h-------</td><td> . 7 hrs________ 24 hrs......</td><td> . Only edge attack. Do.</td>

<td> -80........—</td><td> 3003</td><td> NHiCOj, .48 gm./l_____</td><td> - !, g, h-------</td><td> . 15 min______ 2½ hrs------</td><td> . No attack. . Severe attack in scratches, slight pitting.</td>

<td> 81___________</td><td> 3003</td><td> NH4CO3, .48 gm./l______</td><td> . h___________</td><td> . 15 min...... 2¼ hrs......</td><td> . No attack. . Very severe pitting and attack in scratches.</td>

<td> 82___________</td><td> 3003</td><td> NaaPOi, 1.2 gms./l_____</td><td> . I, g, h-------</td><td> . 15 min______ 45 min______</td><td> . No attack. . Severe attack.</td>

<td> 83.........-</td><td> 3003</td><td> NaaPOi, 1.2 gms./l.....</td><td> . h.._........</td><td> . 15 and 45 min.</td><td> Same as 82.</td>

<td> 84___________</td><td> 3003</td><td> NaaCOa, .50 gm./l_______</td><td> . f, g, h-------</td><td> . 15 and 45 min.</td><td> Do.</td>

<td> 85„-.......</td><td> 3003</td><td> NasCOs, .50 gm./l______</td><td> . h___________</td><td> . 15 and 45 min.</td><td> Do.</td>

<td> 86___________</td><td> HiP</td><td> NaOH, .32 gm./l_______</td><td> . f, g, h-------</td><td> . 5¼ hrs...... 15 lirs_______</td><td> . Edge attack, 2 medium pits on both sides, edge attack. . 10 large pits one side; fairly large area and 3 small pits on other side, severe edge attack.</td>

<td> 87...........</td><td> HIP</td><td> NaOH, .32 gm./l_......</td><td> . h___________</td><td> . 1½ hrs______ 3¼ hrs______</td><td> . Severe attack one side, none other. . Severe attack one side, severe pitting on other.</td>

<td> 88...........</td><td> HIP</td><td> NaaPOi, 1.2 gms./l_____</td><td> . f, g, h------</td><td> . 1½ hrs______</td><td> . Severe attack.</td>

<td> 89...........</td><td> HiP</td><td> NaaCOs, .50 gm./l.... .</td><td> . f, g, h------</td><td> . 1½ hrs ____</td><td> Do.</td>

<td> 90...........</td><td> HiP</td><td> NH4CO3, .48 gm./l_____</td><td> . f, g, h------</td><td> . 4¼ hrs.....</td><td> - Numerous small pits.</td>

3,374,155 oxide coating produced by the sulfuric acid electrolyte step. However as may be noted from specimens of Example 3 which had only a chemically or anodically aluminum oxide coating with or without being sealed in boiling water, the Na_?CO₃ and Na₃PO₄ activation plus further treatment that includes subjecting the specimen to a silicate treatment provided increased corrosion resistance. That is, although Specimens 82-85, 88 and 89 at the interval indicated were severely attacked, the modified coating had not been completely removed.

Also to be noted from Specimens 76 and 78, lower concentrations of Na₂CO₃ and Na₃PO₄ did give better results than higher concentrations of the respective activation solutions.

Further, the high purity specimens (HiP.) that were provided with the modified coating which included Steps (f), (g), and (h) had good corrosive resistance but not as good as the 3003 alloy given the same treatment. Also the high purity specimens that were treated as per the preceding sentence had better corrosion resistance than those in which Steps (f) and (g) has been omitted. This shows that the presence of the iron group metals such as manganese and chromium substantially increases the corrosion resistance. These iron group metals can be incorporated into the final product in three ways:

.(1) Exposing the specimen to a solution such as NiAc₃+FeNH₄ citrate.

(2) Asa constituent in the starting alloy.

(3) As an acid radical in the electrolyte used to provide the aluminum oxide coating in the specimen.

Regardless of the-above manner of incorporating the iron group metals, the activation step plus the silicate treatment step substantially enhances the corrosion resistance over and above that obtained without said steps.

EXAMPLE 8

The effects of varying, the concentration of the basic solution of Procedure A is more fully apparent from the specimens referred to hereinafter in this example. The specimens of Table 21 were, except as noted, treated as follows:

(a) Degreased, 30 second caustic etch, rinsed in water.

(h) Sulfuric acid electrolyte for 30 minutes.

(c) NaOH (concentration of Table 21) for 10 minutes at boiling.

(d) NiAc₃+*FeNH₄C (4.3 gms. each/liter) for 15 minutes at 175-180° F.

(e) MgAc₂ (9.4 gms./liter) for 30 minutes at boiling, (f) Kassil #1 (56 cc./liter) for 30 minutes at boiling.

TABLE 21

<td> Specimen</td><td> Alloy</td><td> NaOH Cone, (gm./l.)</td><td> Elapsed Time (hrs.)</td><td> Corrosion Test Besults</td>

<td> 94 s_________</td><td> 5457</td><td> 1.6</td><td></td><td> - Coating dissolved in</td>

<td> 95 _</td><td> 3003</td><td> 1.6</td><td></td><td> solution c. Do</td>

<td> 96 1_________</td><td> 3003</td><td> 1.0</td><td> 50</td><td> 1 small pit, no attack</td>

<td> 97 1_________</td><td> 5457</td><td> 1.0</td><td> 15</td><td> other side. large areas of severe</td>

<td></td><td></td><td></td><td></td><td> attack as if coating dissolved, other areas</td>

<td> 98__________</td><td> 5457</td><td> .53</td><td> 50</td><td> no attack. 2 pits one side, 6</td>

<td></td><td></td><td></td><td></td><td> medium and few small</td>

<td> 99__________</td><td> 3003</td><td> .53</td><td> 50</td><td> pits on other. 2 small pits one side, 2</td>

<td> 100 2________</td><td> 5457</td><td> .53</td><td> 50</td><td> medium pits on other. No attack.</td>

<td> 101²________</td><td> 5457</td><td> .53</td><td> 50</td><td> A few small pits on</td>

<td> 102_________</td><td> 5457</td><td> .32</td><td> 48</td><td> both sides. No attack except at</td>

<td> 103_________</td><td> 3003</td><td> .32</td><td> 48</td><td> edges. Do.</td>

<td> 104³________</td><td> 5457</td><td> .25</td><td> 3</td><td> Attack between</td>

<td></td><td></td><td></td><td></td><td> splotches, otherwise</td>

<td> 105_________</td><td> 5457</td><td> .20</td><td> 3</td><td> OK. Attack around edge and</td>

<td> 106_________</td><td> 3003</td><td> .10</td><td> 3</td><td> bottom. Very severe pitting</td>

<td></td><td></td><td></td><td></td><td> attack over entire</td>

<td> 107 3________</td><td> 3003</td><td> .10</td><td> 3</td><td> area. Do.</td>

<td> 108 «________</td><td> 3003</td><td> .10</td><td> 3</td><td> Similar but somewhat</td>

better than 106,107.

(1) (2) (3) (4) (5)

Specimens 96, 97 -----Reddish color on lower part after treatment to solution (d).

Specimens 100, 101 ___ Reddish color after treatment to solution (d).

Specimens 104, 107 ___ Subjected to a 3 minute chromic acid electrolyte just after the sulfuric acid electrolyte treatment.

Subjected to a 5 minute chromic acid electrolyte just after the sulfuric acid „ . electrolyte treatment.

Specimens 94, 95 -----Not treated per Procedures

B, C and D.

Specimen 109 was degreased, bright dipped, treated for one hour in a sulfuric acid electrolyte, and treated to the solutions as follows:

Specimen 108

NaOH (.15 gm./liter)___________

NiAcj (8.9 gm./liter)________

NaiSlOa (liq G.T.W. 42 ce./literY min------- 120-140° F.

mln------ 120-140° F.

hour 212° F.

After 10½ hours in the corrosion test both sides were attacked only in the scratches on the specimen.

For each of the specimens of Table 21, an observation was made at the end of the treatment in solution (c) to ascertain the effects of varying the concentration of solu^tlO4 ίη/Λ⁰/ ^each,^of Specimens 102, 103 (.32 gm./liter) and 104 (.25 gm./liter) it was noted that the anodic aluminum oxide coating was severely attacked by the activating solution while Specimen 105 (.20 gm /liter) showed considerable attack and 106-108 (.10 gm’./liter) had no noticeable attack. With 1.6 gms./liter, the anodic aluminum oxide coating was completely dissolved, i.e. Specimens 94, 95. This shows that the concentration of the activating solution and the time and temperature cannot be such that the aluminum oxide coating is too severely attacked; otherwise the subsequent treatment steps will not provide best results. On the other hand, too low a concentiation (considering time and temperature) apparently does not properly condition the aluminum oxide coating for further treatment. The aforegoing is to be taken in consideration with the corrosion test results after the specimens had been treated as per Procedures B, C and D which indicated the finally treated specimens Specimens 96 and 98-103 had the best corrosion resistance. Also contrast Specimen 95 with 96. Using NaOH for the activating solution of approximately .3-.55 gram/liter at boiling for 10 minutes has given best results while .15-1.0 gram/liter normally give satisfactory results. Of course the thicker aluminum oxide coating can withstand a more severe attack by the actuating solution than a thinner coating.

As to the observations after the NiAc₃+FeNH₄ citrate treatment it was noted that each of Specimens 102-104 were discolored while there was no discoloration of Specimens 106-108. In order to avoid this discoloration the NiAc₃FeNH₄ citrate solution should be kept at about 160-170° F. . ^r

With reference to the edge attack on Specimens 103, 105 and 108 before the activation treatment, the edges were sponged with degreaser to attempt to remove fingerprints. On the basis of this, it appears that some of the edge attacks and attack in the form of splotches results from handling the specimens and points out that the specimens should be kept free of oil and grease during the treatment thereof.

A series of specimens were pretreated and subjected to a sulfuric acid electrolyte treatment for 40 minutes. They were then treated in a NaOH solution of .30' gm./liter for 5 minutes at various temperature ranges of 120-140° F., 160-180° F. and violent boil respectively, next treated to a solution of NiAc₃4~FeNH₄ citrate (4.3 gms. each/ liter) for 15 minutes at 120-140° F. and then to liquid

3,374,155

GTW silicate (56 cc./liter) for one hour at boiling. The specimens were subjected to a corrosion test, Specimen 110 which was treated in a violent boil solution showed no attack at 4 hours, and 2 small pits together with some edge attack at 21 hours. Specimen 111 which was treated at 160-180° F. had some bottom attack on one side and few pits on the other at 4 hours while at 14 hours had numerous small pits on one side and very few small pits on the other. Specimen 110 had the best corrosion resistance with 111 second best.

It was noted that heating at the low temperatures resulted in bubbles clinging to the specimen surface in a pattern that generally appeared similar to the pattern of attack in the subsequent corrosion test. The violent boil attack in scratches, and after 8½ hours numerous small pits and attack along scratches on both sides.

With reference to the specimens of Table 22, all of these specimens were first degreased, given a 30-second caustic etch, rinsed in water, treated in a sulfuric acid electrolyte for 30 minutes, rinsed in water and then treated in the solutions as follows:

(a) NaOH (.29 gm./liter)____________________10 mm------,¾¹½ „ (b) NiAc_s+*FeNHjC (4.6 gms. each/litcr) _. 15 mm------1«Μ·θθ 1'· (c) MgAcz (9.4 gms./liter)-------------------30 min------Boiling.

(d) Silicate solution (56 cc./liter)------------30 min------ -Do.

Afterwards these specimens were subjected to the corrosion test.

TABLE 22

Specimen Alloy Type Silicate Elapsed

Time (hrs.)

Corrosion Test Results

<td> 112_______</td><td> 5457</td><td> N______________</td><td> 20</td>

<td> 113_______</td><td> 3003</td><td> N______________</td><td> 20</td>

<td> 114.......</td><td> 5052</td><td> N..............</td><td> 20 14 15</td>

<td> 115_______</td><td> 5457</td><td> S-35___........</td><td> 20 14 15</td>

<td> 116_______</td><td> 3003</td><td> S-35___________</td><td> 20 14 15</td>

<td> 117_______</td><td> 5052</td><td> S-35__________</td><td> 20</td>

<td> 118_______</td><td> 5457</td><td> Kassil #1______</td><td> 20</td>

<td> 119_______</td><td> 3003</td><td> _____do________</td><td> 20</td>

<td> 120_______</td><td> 5052</td><td> _____do--------</td><td> 20</td>

Slight pitting one side, no attack other.

Few small pits.

pit one side, 5 on other, scratches not pitted.

No attack.

Some pits noted.

Numerous small pits.

No attack.

Some pits.

A few small pits, scratches pitted.

No attack.

Some pits.

Severe pitting in scratches some attack on coating.

Few small pits one side, none other.

pit one side, 2 on other, scratches not pitted.

No pits one side, 3 other, scratches not pitted.

kept the 110 specimen surface free from bubbles and it better withstood attack. This shows that during the activation step, the solution should be either mechanically or otherwise agitated to keep bubbles from clinging to the article being treated to obtain best results.

EXAMPLE 9

As shown by Specimens 112-120, Kassil #1 gave better results than N-silicate and S-35 silicate. Although some of the pits in these specimens may have occured at defects in the specimens, the overall performance of Kas40 sil # 1 is somewhat better than that of N-silicate and considerably better than the S-35 silicate. In this connection it is noted that the respective ratios of percent

Various silicate solutions were tested to ascertain the 45 effects of varying the type silicate used. A number of specimens (3003 alloys) were degreased, caustic etched and then subjected to a sulfuric acid electrolyte for 1 hour. Thus these specimens were successively treated with the following:

K₂O:%SiO₂ and percent Na₂O:SiO₂ for Kassil #1, N-silicate and S-35 silicate are respectively 1:2.50·; 1:3.22; and 1:3.75.

NaOH (.15 gm./liter)----------------------NiAci+FeNH.iC (4.3 gms. eacb/liter)------MgAcs (9.4 gms./liter)---------------------5 mln_______120°-140° F.

min______120°-140° F.

min______212° F.

The specimens then treated with liquid GTW, a sodium silicate showed less attack than those treated with Metso 99 silicate which in turn were better than those treated with G.D. silicate or sodium metasilicate. With reference to the specimen treated with liquid GTW silicate, after 7 hours in the corrosion test it had slight pitting and slight

EXAMPLE 10'

A series of specimens were treated in order to determine the effects of varying the concentration of the silicate solution, these specimens being set forth in Table 23. The specimens of Table 23 were treated the same as those of Table 22 except that only Kassil #1 of the congo centrations of Table 23 were used and for specimens 124 and '122 a foaming agent was added to the electrolyte solution before the anodic treatment.

TABLE 23

Specimen Alloy Silicate Elapsed Corrosion Test Results

Concentration Time (hrs.)

<td> 121_______</td><td> 5052</td><td> 14 cc./liter_______</td>

<td> 122_______</td><td> 5457</td><td> _____do__________</td>

<td> 123_______</td><td> 5052</td><td> 28 cc./liter.......</td>

<td> 124_______</td><td> 5457</td><td> _____do__________</td>

<td> 125_______</td><td> 5052</td><td> 56 cc./liter.......</td>

<td> 126_______</td><td> 5457</td><td> _____do__________</td>

A few pits and attack in scratches, 7 pits other.

A few pits and attack in scratches, other few medium size pits.

' 5 pits one side, other 5 pits and attack in scratches.

Medium number of pits one side', numerous pits on other.

No attack one side, few small pits on other.

A number of pits one side, 4 pits on scratches on other.

3.374.155

A concentration of 56 cc./liter of Kassil #1 was somewhat better than 14 cc. and 28 cc. per liter.

EXAMPLE 11

The specimens of this example are primarily directed to variations in Procedure B. However various specimens of the other examples show additional variations in this procedure (in particular note Example 21 and the ones that follow), and some of the specimens of this example are pertinent relative showing conditions of treatment for other procedures of this invention. All the specimens of this example were pretreated to condition them for a sulfuric acid electrolyte treatment of a duration set forth in Table 24. After the anodic treatment and rinsing in water, the specimens were successively treated to the solutions indicated in Tables 25 and 26 with a water rinse prior to Procedure D and thereafter. The results of the NaOH corrosion test after the treatment indicated in Tables 25 and 26 are set forth in Table 24.

TABLE 24 „ . ElecSpecimen Alloy trolytic

Treatment

Time Elapsed (hrs.)

Corrosion Test Results

<td> 127________ 128________</td><td colspan="2"> --------------45 min____ --------------1 hr_______</td><td> 7 22 5</td>

<td> 129.......</td><td> 5457</td><td> 40 min _. _</td><td> 19</td>

<td> 130________</td><td></td><td> ... lhr_______</td><td> 9</td>

<td> 131________</td><td> ------------</td><td> ... 40min_...</td><td> 18 2 3 7½</td>

<td> 132_________</td><td> ............</td><td> 40 min____</td><td> 10½ 2 3</td>

<td> 133-.._____</td><td></td><td></td><td> 2 3</td>

<td> 134_________</td><td></td><td></td><td> 2 3 7½ 10¼</td>

<td> 135_._......</td><td></td><td></td><td> 10 20</td>

<td> 136_________</td><td> —</td><td></td><td> 8</td>

<td> 137, 138.--.</td><td> 3003</td><td> 1 hr_______</td><td> 13 13 20</td>

<td> 139.........</td><td> 5457</td><td> 1 hr________</td><td> 13 20</td>

<td> 141_________</td><td> 5457</td><td> 1 hr.______</td><td> 13 20</td>

<td> 142_________</td><td> 3003</td><td> 40 min_____</td><td> 20</td>

<td> 143_________</td><td> 5457</td><td> 40 min____</td><td> 20</td>

<td> 144_________</td><td> 5457</td><td> 40 min___.</td><td> 19</td>

<td> 145_________</td><td> 5457</td><td> 1 hr_______</td><td> 15</td>

<td> 146___________</td><td> 5457</td><td> 40 min_.__</td><td> 20</td>

<td> 147.....</td><td> 3003</td><td> 30 min___.</td><td> 20</td>

<td> 148________</td><td> 3003</td><td> 30 min-...</td><td> 20</td>

<td> 149_________</td><td> 5052</td><td> 30 min____</td><td> 11</td>

<td> 150..........</td><td> 5457</td><td> 30 min____</td><td> 20</td>

<td> 151________</td><td> 5457</td><td> 30 min....</td><td> 20</td>

<td> 152__________</td><td> 5457</td><td> 30 min....</td><td> 11</td>

<td> 153.___a______</td><td> 5457</td><td> 30 min_.__</td><td> 20</td>

<td> 154..........</td><td> 3003</td><td> 30 min_.._</td><td> 20</td>

<td> 155__________</td><td> 5052</td><td> 30 min_._.</td><td> 20</td>

<td> 156-_________</td><td> 5052</td><td> 30. min______</td><td> 15</td>

<td> 157__________</td><td> 5052</td><td> 30 min_...</td><td> 20 20</td>

<td> 158......</td><td> 3003</td><td> 30 min_____</td><td> 20</td>

<td> 159..........</td><td> 5457</td><td> 30 min______</td><td> 20</td>

<td> 160__________</td><td> 5457</td><td> 30 min___.</td><td> 32</td>

<td> 161.......</td><td> 5052</td><td> 30 min....</td><td> 32</td>

<td> 162..........</td><td> 3003</td><td> 30 min..._</td><td> 32</td>

<td> 404__________</td><td> —</td><td> . 45 min.._.</td><td> 3 4½ 6 11</td>

Negligible attack.

Localized attack at what appeared to be fingerprints on specimen and some small pits.

^one side had attack in scratches and m one area that appeared touched by fingers.

Numerous small pits on both sides.

No noticeable attack.

Considerable attack and pitting.

No attack.

Practically none.

Slight attack on both sides.

Medium pits both sides.

No attack.

Has considerable attack.

No attack.

Considerable attack.

No attack.

Practically none.

Slight pitting on one side, severe pitting on other.

Numerous pits on one side, severe pitting on other.

No attack except edges where touched testing racks.

Some medium size pits also large areas no attack.

Pew small pits one side and few pits and attack along scratches on other.

Same except more attack along scratches.

Slight attack.

Numerous small pits both sides, large areas of no attack.

No attack.

Large areas no attack, large pits one side smaller pits on other.

No attack.

Large areas no attack, large pits one side; smaller pits on other; 134 better than 141.

pits one side, none other, attack in scratches.

Very few small pits except on sides and bottom.

A few small pits and attack along scratches.

Few scattered pits on one side, numerous medium size pits and attack in scratches.

Small pits more numerous than 143 but still very good.

Numerous shallow fine pits on both sides.

Medium number of pits on both sides.

One side severe attack along scratches other medium number of small pits.

Some attack on side otherwise no attack.

Only small area attack on one side.

Medium number of pits both sides.

Very slight pitting, appeared associated with dent in sample.

Same as 153.

Do.

No noticeable attack.

Numerous small pits.

Slight pitting near bottom otherwise OK Do.

Slight pitting, except where touched by fingers on one side.

small pits one side, very few pits on other, very good condition.

small pits each side, otherwise no attack.

No attack except where touched in corner.

No attack.

pits and attack in small scratch one side, no attack other.

Same on said one side, 1 pit other.

pits and edge attack one side, 3 pits other.

large pits and edge attack one side, 3 pits other.

3,374,155

TABLE 25

Specimen

Procedure A

127___________

128...........

129...........

130___________

131...........

132___________

133...........

134___________

135__________

136__________

137___________

138...........

1391__________

141___________

142...........

143-.-........

144___________

145...........

146—........

147...........

148...........

149___________

150___________

151___________

152...

153-

154.

155..........

156—......

157, 158, 159.

160, 161, 162.

404..........

NaOH (.26 gms.A.).

NaOH (.15 gms./l.).

NaOH (.30 gms./l.).

NaOH (.26 gms./l.).

NaOH (.15 gms./l.).

NaOH (.15 gms./l.).

NaOH (.15 gms./l.).

NaOH (.15 gms./l.). NaOH (.15 gms./l.). NaOH (.15 gms.A·). NaOH (.15 gms./l.). NaOH (.15 gms./l.). NaOH (.15 gms./l.). NaOH (.15 gms./l.). NaOH (.30 gms./l.). NaOH (.30 gms./l.). NaOH (.30 gms./l.). NaOH (.30 gms./l.). NaOH (.30 gms./l.). NaOH (.28 gms./l.). NaOH (.28 gms./l.). NaOH (.28 gms./l.). NaOH (.28 gms./l.). NaOH (.28 gms./l.). NaOH (.28 gms./l.), NaOH (.28 gms./l.), NaOH (.28 gms./l.), NaOH (.28 gms./l.), NaOH (.28 gms./l.), NaOH (.28 gms.A·). NaOH (.28 gms./l.). NaOH (.30 gms./l.).

<td> u (Activation)</td><td></td><td> Procedure B</td><td></td><td></td>

<td> 5 min_______</td><td> 120-140° F—</td><td> .. NiAcs (5 gms./liter). --------------------------</td><td> ... 15min_...</td><td> ... 120-140° F.</td>

<td> 5 min ... ..</td><td> 120-140° F—</td><td> ZnAcj (8.9 gms./liter)--------------------------</td><td> ... 15 min____</td><td> ... 120-140° F.</td>

<td> 5 min. .....</td><td> 212° F_______</td><td> .. NiAcs (8.9 gms./liter)..........................</td><td> ... 15 min....</td><td> ... 120-145° F.</td>

<td> 5 min_______</td><td> 120-140° F—.</td><td> .. NiAcs (5 gms./liter)---------------------------</td><td> ... 15 min____</td><td> ... 120-140° F.</td>

<td> 5 min ______</td><td> 120-140° F...</td><td> .. NiAca (8.9 gms./liter)__________________________</td><td> ... 15 min_...</td><td> ... 120-140° F.</td>

<td> 5 min ______</td><td> 120-140° F„.</td><td> .. MgAcs (8.9 gms./liter).........................</td><td> ... 15 min_._.</td><td> ... 120-140° F.</td>

<td> 5 min ______</td><td> 120-140° F.._</td><td> .. PbAc₂ (8.9 gms./liter)-------------------------</td><td> ... 15 min....</td><td> ... 120-140° F.</td>

<td> 5 min.......</td><td> 120-140° F—</td><td> .. MgAc3 (8.9 gms./liter).........................</td><td> ... 15 min....</td><td> ... 212° F.</td>

<td> . 5 min_______</td><td> 120-140° F—.</td><td> .. NiAca (8.9 gms./liter)__________________________</td><td> ... 15 min....</td><td> ... 120-140° F.</td>

<td> 5 min_______</td><td> 120-140° F—.</td><td> .. CrAcs (8.9 gms./liter)..........................</td><td> .. 15 min____</td><td> ... 120-140° F.</td>

<td> 5 min .. . .</td><td> 120-140° F...</td><td> . CrAcs+KsCjO? (4.5 gms. each/liter)-----------</td><td> ... 15 min. — .</td><td> ... 120-140° F.</td>

<td> 5 min .. . .</td><td> 120-140° F—.</td><td> .. CrAca+KMnOi (4.5 gms. each/liter) —.......</td><td> .. 15 min....</td><td> ... 120-140° F.</td>

<td> . 5 min ______</td><td> 120-140° F—.</td><td> . CrAcs+KsCsO? (4.5 gms. each/liter)-----------</td><td> ... 15 min....</td><td> ... 120-140° F.</td>

<td> 5 min _____</td><td> 120-140° F—.</td><td> . CrAcs+KMnOi (4.5 gms. each/liter)-----------</td><td> ... 15 min....</td><td> ... 120-140° F.</td>

<td> 10 min ....</td><td> 212° F_______</td><td> . NiAcs-pFeNILiC (4.3 gms. each/liter)--------</td><td> ... 30 min....</td><td> ... 120-145° F.</td>

<td> 10 min _____</td><td> 212° F._.....</td><td> .. NiAcs+MgAcj (4.3 gms. each/litcr)------------</td><td> ... 15 min____</td><td> ... 120-145° F.</td>

<td> 5 min.......</td><td> 212° F_______</td><td> .. NiAea-i-^FeNHiC (4.3 gms. each/liter)--------</td><td> ... 15 min...</td><td> ... 120-145° F.</td>

<td> . 10 min______</td><td> 212° F_______</td><td> .. ZnAcj (4.1 gms./liter)--------------------------</td><td> ... 15 min...</td><td> ... 120-140° F.</td>

<td> 5 min ......</td><td> 212° F_______</td><td> . NiAc3+*FeNHiC (4.3 gms. each/liter)________</td><td> ... 15 min...</td><td> ... 120-140° F.</td>

<td> 10 min_____</td><td> Boil_________</td><td> .. NiAc3-i-*FeNH4C (4.6 gms. each/liter)--------</td><td> ... 15 min....</td><td> ... 130-150° F.</td>

<td> 10 min ....</td><td> Boil_________</td><td> .. NiAc3-F*FeNH4AC2 (4.6 gms. each/liter)______</td><td> .. 15 min...</td><td> ... 130-150° F.</td>

<td> 10 min _____</td><td> Boil_________</td><td> .. NiAcj-pFeNHjC (4.6 gms. each/liter)--------</td><td> 15 min....</td><td> ... 120-140° F.</td>

<td> 10 min......</td><td> Boil_________</td><td> ______do_________ - ------------------</td><td> ... 30 min____</td><td> ... 120-140° F.</td>

<td> . 10 min......</td><td> Boil_________</td><td> ______do--------------------------------------—</td><td> ... 30 min___</td><td> ... 120-140° F.</td>

<td> . 10 min______</td><td> Boil_________</td><td> —. ...do_________________________________________</td><td> . . 30 min___</td><td> ... 120-140° F.</td>

<td> . 10 min ....</td><td> . Boil_________</td><td> .......do........................................</td><td> „. 15 min...</td><td> ... 150° F.</td>

<td> . 10 min. ....</td><td> Boil_________</td><td> ________do. --------------------------------------</td><td> ... 15 min___</td><td> ... 150° F.</td>

<td> . 10 min.. ...</td><td> Boil_________</td><td> _______do ---------------------------------------</td><td> ... 15 min___</td><td> ... 150° F.</td>

<td> . 10min ... .</td><td> Boil_________</td><td> _______do.— ...................................</td><td> ... 15 min...</td><td> ... 146° F.</td>

<td> 10 min______</td><td> Boil_________</td><td> _______do________________________________________</td><td> . 15 min...</td><td> ... 158-162° F.</td>

<td> 10 min......</td><td> 250° F_______</td><td> _____.do________________________________________</td><td> ... 15 min___</td><td> ... 148° F.</td>

<td> . 10 min______</td><td> Boil_________</td><td> .. NiAc3+*FeNH4Ac2 (4.9 gms. each/liter)_______</td><td> ... 15 min...</td><td> ... 155-165° F.</td>

TABLE 26

Specimen Procedure C

Procedure D

127____________None______________________

128____________MgAcs (8.9 gms./liter)----129_________________do-------------------130____________None______________________

131_________________do--------------------132_________________do--------------------133_________________do--------------------134_________________do--------------------135____________MgAc₂ (8.9 gms./liter)----136_________________do-------------------137_________________do____________________

138_________________do-------------------139_________________do-------------------141_________________do-------------------142_________________do____________________

143_________________do____________________

144_________________do-------------------145______ do____________________

146____________MgAc (8.9 gms./liter-----147,148_______MgAc (9.4 gms./liter)----149_________________do____________________

150_________________do-------------------151_________________do-------------------152_________________do____________________

153_________________do-------------------154_________________do-------------------155_________________do-------------------156_________________do-------------------157,158,159.- None_____________________

160, 161, 162... MgAc2 (9.4 gms./liter)----404 MgAc₂ )9.8 gms./liter)----______________________________Liq. G.T.W. (28 cc./liter)_______________________ min......212° F......... Liq. G.T.W. (42 cc./liter)_______________________ min______212° F„.......Na₂SiO₂ (56 cc./liter)____________________________ ______________________________Liq. G.T.W. (28 cc./liter).______________________ ___________________________________do__________________________________________ .do .do.

min______212°F_.

min______212°F..

min______212°F_.

min......212°F_.

min......212°F_.

min______212°F_.

min......212°F_.

min......212°F_.

min______212°F..

min______212°F..

min______212°F_.

min______Boil—..

min...do.

mindo.

min______do.

mindo.

min..do.

min...do.

min.do.

mindo.

min...... 250° F__________ min...... 200° F.........

_____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________

Liq. G.T.W. (56 cc./liter)_______________________ ____.do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________ _____do_____________________________________..... _____do__________________________________________ _____do..________________________________________ _____do__________________________________________ _____do__________________________________________ _____do__________________________________________

Kassil #1 (56 cc./liter)___________________________ _____do__________________________________________

Kassil #1 (27 cc./liter)___________________________ hr_________212° F.

hr_________212° F.

hr.........212° F.

hr_________212° F.

br__....... 212° F.

hr.........212° F.

hr_________212° F.

hr.........212° F.

hr_________212° F.

hr......... 212° F.

hr_________212° F.

hr.........212° F.

hr.........212° F.

hr........ 212° F.

hr.........212° F.

hr_________212° F.

hr_________212° F.

hr.........212° F.

hr_________212° F.

minBoil.

min. Do.

min......212° F.

hr......... 212° F.

hrBoil.

min______212° F.

min......212° F.

min______212° F.

min______212° F.

min______Boil.

min______ 250° F.

min...... 200-212° F.

COMMENTS 60 (1) A comparison of test runs with Specimen 143 (only variation in time in the activating solution of Procedure A) indicated that 10 minutes as contrasted to 5 minutes give improved resistance to corrosion. 65 (2) From this example and others, it appears that alloy 5052 gives somewhat better results with a coating procedure that includes at least Procedures A and D than alloys 3003 and 5457.

(3) A comparison of Specimens 129 and 144 show that the addition of ferric ammonium citrate to the nickel acetate increases the corrosion resistance; while other tests indicate that varying the time of treatment in the NiAc₃+FeNH₄ citrate solution between 15 and 30 minutes, the 30-minute treatment increased the corrosion re sistance of the final coating over that of the 15-minute treatment.

(4) A comparison of Specimens 157-159 (NiAc₃+FeNH₄ citrate at 158-162° F.) versus 19-20 of Example 2 (same solution at 178-180° F.) shows that the higher temperature, i.e. 180° F. gives better results than the lower temperatures. However increasing the temperature from 180° F. to boiling did not improve the corrosion resistance, compare Specimens 98, 99 (Example 8) with Specimens 100, 101 (Example 8); and that the coating was discolored, Specimens 100, 101 having a reddish color after being treated to the boiling solution of NiAc₃+FeNH₄citrate. In view of the fact that for some applications, discoloration is undesirable, it is desirable that the solu3,374,155

<td> 29 tion of Procedure B be at a temperature of about 140180° F. and preferably about 155-165° F. (5) Test such as for Specimens 12, 14, 15 (Example 2); 145 (Example 11) and 192 (Example 14) indicate that using ZnAc₂ and MgAc₂, or NiAc₃+FeNH₄ citrate and 5 BaAc₂ in the solutions of Procedures B and C respectively, does produce accepted results but not as good as the NiAcs+FeNHt citrate and MgAc₂ treatment. With reference to using MgAc₂ in Procedure C also note Example 14. Further using NiAc₃+FeNH4 citrate gives more , _nconsistent results than using either of these compounds by itself in Procedure B.</td><td> 30 ___________________ TABLE 28 _o . Procedure Specimen ____________._____________ B Sol. C. Sol. D Sol. 173, 174----------- 160-170° F_______Boil_____ Boil 175, 176, 177------- 160-170° F______ 250° F_ 250° F 178--------------- 150-170° F.------ 160-170° F_. Boil 179-------- 150-170° F_______ 180-190° F____ 250° F 180, 181, 182-------- 160° F----------- 200-212° F_______ 200-212° F. TABLE 29</td>

<td></td><td> Time Specimen Alloy Elapsed Corrosion Test Results</td>

<td> EXAMPLE 12</td><td> 15---------------------—_________________ 173--------- 5052 22 Medium pitting on both sides. U4--------- 5052 22 No attack except on bottom adge.</td>

<td> A series of specimens all were first degreased, given a caustic etch and then a 45-minute sulfuric acid electrolyte treatment. Specimens 166, 168, 169 were additionally then subjected to a 3-minute chromic acid electrolyte while Specimens 167, 172 were subjected to a five minute chromic acid electrolyte. The specimen alloys were as</td><td>^&lt;,J--....... ^ΰυυό Large areas of severe attack in H of width of specimen, the other H . _ no attack. i/b. ------- 5052 21 Some areas of severe attack on % of 20 specimen, no attack on other third. 177--------- 3003 21 Some large areas near side to bottom showed severe attack on the steel wooled side; while the other side was attacked after 2 hours in the</td>

<td> 3003: 164, 168, 171. 5052: 165, 169, 172. 5457: 163, 166, 167, 170. After the electrolyte treatment each specimen was treated in NaOH solution of a concentration of .26 gm./ liter for 10 minutes at boiling and just before the corrosion test to a silicate treatment of Kassil #1 (28 cc./liter) at boiling for 30 minutes. Intermediate the activation treatment and the silicate treatment the specimens were treated as follows:</td><td> test solution and the whole side was etched IS through the thick_17S . ness of the specimen. 178--------- 5052 5 No attack. 6 2 pits one side, no attack other. 23 The side of the 6 hr. pits increased and two more started on one side and 5 small ones on the other. 30 179.... 3003 5 No attack. 6 Numerous pits one side, few pits on other side near bottom and 180--------- 3003 20 No attack one side, 2 small pits I qi oorm on other. lei----------- .3003 20 1 small pit one side, other one small pit and slight attack in ^ΰυ iqo scratches.</td>

<td> TABLE 27</td><td>^δ--------- ^{5052 16} Medium pitting one side, slightly ______less on other.</td>

<td> Specimen Further Treatment Time Temperature (mln.) 163, 164, 165... NiAca+FeNIL citrate (4.9 15 160-170° F gms./l.). Than MgAca (9.8 gms./l.)________ 30 Boilinc 166,169-------MgAez (9.8 gms./l.)... 1..________ 30 Do. 170-172-------CrAc3+*FeNH4C (4.6 gms. 15 160-170° F each/1.). ________ Than MgAc₂ (9-8 gms./l.)........ 30 Boiling</td><td> 40 It. was noted a heavy gelatinous coating was on the specimens 175-177 which were heated in MgAc₂ at 250° F. This coating was removed by steel wool on both sides of 175 and one side each of 177 and 176. In other tests some gelatinous coating was noticed when treating speci- 45 mens to a boiling solution of MgAc₂ but not nearly as heavy .as when heating at 250° F. These examples clearly indicate that the gelatinous product from the MgAco</td>

<td> The results for these specimens after the 1% NaOH corrosion test indicated that the modified oxide coating formed by the steps for Specimens 163-165 was the best. Further relative Procedure B, using either CrAc₃ or NiAc_s with FeNH_t citrate yields substantially the same results, i.e. no substantial difference in using CrAc_s or NiAc₃ (compare Specimens 123, 124 Example 10, with Specimens 24 of Example 2 and 41 of Example 4).</td><td> treatment affects the corrosion resistance and must be ^{t0 yieId 8}°°^{d resuIts}- However note Specimens 50 160, 161, .162, Example 11, which show that good results were obtained when heating the MgAc₂ solution at 250° ^NaOH solution of Procedure A also being at ^ref^erence to Specimens 178 and 179, no gelatinous •io precipitate was noticed after the MgAc₂ 150-160° F. treatment but considerably for the 180-190° F treatment.</td>

EXAMPLE 13

The series of specimens of Tables 28 and 29 were tested to in part determine the effect of varying the temperature of the Procedure C solution. All of these specimens were first pretreated and subjected to a 45-minute sulfuric acid electrolyte treatment, specimens 173 and 177 then being sealed in boiling water for 15 minutes. All of these specimens were then successively treated in solutions as follows:

Some of the pits of Specimen 182 are at the scratches or metal defects.

In view of results such as obtained for Specimens ISO182 and Specimens of other Examples 200-212° F for Procedure C is preferred.

NaOH (.32 gms./liter)_________________

NiAc3+*FeNH₄C (4.9 gms. each liter) MgAca (9.8 gms./liter).....__________....

Kassil #1 (56 cc./liter) min....

min.___ min.___ min....

Boiling.

See Table 28.

Do.

Do.

EXAMPLE 14

In order to determine the effect of using various acetates tor procedure C solutions, all the specimens of Table 70 30, which were a 3003 alloy were first subjected to the steps successively as follows: degreased, flash sulfuric acid electrolyte for one minute, and a 15-second caustic etch, a sulfuric acid electrolyte for 45 minutes, rinsed in water and then to an activating solution of NaOH of 75 about .32 gram per liter of water at boiling for 10 min3..374,155 utes. The further treatment and the results of the 1.0% NaOH corrosion test are as follows:

sequent precipitating of the silica was noticed in the areas attacked.

TABLE 30

<td> Specimen</td><td> B</td><td> C</td><td> D</td><td> Time</td><td> Results</td>

<td> 183__________ 184__________ 185__________ 186__________ 187__________ 188-........ 189_________ 190_________ 191_________</td><td> NiAc+’FeNHiC.... NiAc+’FoNIIiC... . NiAc+’FcNILC... . NiAc+’FeNHjC... . NiAc+’FeNHjC-- . NiAc+’FeNHjC... . NIAc+*FeNHjC--. . NiAc+’FeNHtC—. . NiAe-PFeNHjC...</td><td> MgAc2_____ __ KAc_______ CaAcs_____ ... BaAc2_____ -_ ZnAcz______ ... MgAc2_____ . MgAc2_____ ... MgAcj_____ ... KAc_______</td><td> ... Kassil #1___________ ________do __________ ________do______________ ________do_____________ ________do_____________ ... Boiling H2O seal... .... Kassil#!........... .........do............. .........do_____________</td><td> ...1¼ hrs______ ... 1¼ hrs______ 5¼ hrs______ 8 hrs________ 17 hrs_______ ... 1¼ hrs______ 5¼ hrs______ 8 hrs________ 17 hrs_______ ... 1¼ hrs______ 5¼ hrs__.... 8 hrs________ 17 hrs_______ --_ 1¼ hrs______ 5¼ hrs______ 8 hrs........ 17 hrs_______ ___ 10 min______ 17 min______ --.26 hrs....... -..26 hrs_______ .-.26 hrs_______</td><td> ... Severe attack similar to that as when Ac solution to acid. ... No attack. ... 3 pits one side, 1 pit other, attack in scratches. ...3 pits one side, 2 pits other, attack in scratches. ... 8 large pits, 15 small one side, 3 large pits, 3 small other, severe attack in 2 scratches. ... No attack. ...5 pits and 2 scratches attacked one side, 2 pits other side. ...13 pits and 3 scratches one side, 6 pits and one scratch other side. ... 20 pits one side, 15 pits other, severe attack in. scratches both sides.· — No attack. ... Only attack in scratches on one side. .__4 small pits one side, severe attack in scratches both sides, severe attack in scratches and near edge. __ 10 pits one side, sever attack in scratches and near edge. ... No attack. ... Only small pits on one side. ... Number of small pits one side, 2 large areas of attack and a number of small pits on other side. ... Very severe attack and pitting on both sides. __ No attack. ... Very severe attack. ... No attack. Do. Do.</td>

With reference to Table 30 the concentrations of the solutions and other conditions other than those given above are as follows:

Concentration

Time Temperature

NiAcs-pFeNHiC (4.9 gms. each liter)----15 min-----MgAca (9.8 gms./liter)................ 30 min......

Kassil #1 (28 cc./liter).....................

KAc (9.5 gms./liter)......................

CaAc2 (9.5 gms./liter)_____________________

BaAc2 (9.5 gms./liter)—...................

ZnAc2 (9.5 gms./liter)............-........

min______ min______ min______ min______ min______

160° F.±5° F.

200° F. but not boiling.

Do.

Do.

Do.

Do.

Do.

Specimen 192 (5457 alloy) was degreased, caustic etched, bright dipped, subjected to the sulfuric acid electrolyte treatment for one hour and then treated to the solutions as follows:

Concentration

Time Temperature

NaOH (.30 gms./liter)____________________10 min------212° F.

NiAcj+’FeNHjC (4.3 gms. each/Uter).... 15 min------ 120-140° F.

BaAcj (8.1 gms./liter)_____________________30 min------212° F.

Liq. G.T.W. (56 cc./liter) 1 hr---------212° F.

At 7 hours in the corrosion test, Specimen 192 had numerous small pits on both sides.

With reference to specimens 184-187 the KAc treatment gives the best results followed by CaAc₂ which specimen had attack in the scratches but considerable parts unattacked. The ZnAc₂ specimen had the poorest corrosion resistance of this group, there being considerable pitting and large areas attacked.

With reference to specimen 186 it is thought that BaSO₄ could have precipitated and prevented the Kassil #1 properly reacting with the aluminum oxide. With reference to the relatively early attack in the scratches of these specimens and others, a possible explanation is that some acid from the electrolyte treatment was retained therein and caused the precipitation of silica from the silicate treatment step.

Prior to carrying out Step C of the example, it was determined that each of the KAc, CaAc₂ and BaAc₂solutions were slightly acid while the ZnAc₂ solution was very acid. The areas of attack on the ZnAc₂ specimen were typical of an acid condition wherein the subWith reference to the severe attack of Specimen 183 in a short time, it was unexplained. In running another test with a specimen from the same sheet of metal as ³³ Specimen 183 it was noted the surface was dull before pretreatment which indicates that there was present a rather thick film of aluminum oxide from atmospheric oxidation. It appears probable that this thick film was on Specimen 183, and not completely removed prior to ⁴⁰ the anodic treatment.

Also with reference to Specimen 183 the MgAc₂ solution used had been previously used. Accordingly before Specimens 189-191 were treated as indicated above, the MgAc₂ solution that had been used for Specimen 183 ⁴³ was first titrated with sufficient NaOH solution to make the solution basic and this titrate solution was used for Specimen 190, while freshly made MgAc2 solutions were used for treating specimens 188 and 189. Also a new solution of NiAc3+FeNH4 citrate was used, which was ³θ basic for Specimens 188-191. As indicated in the results for the last mentioned specimen (contrast to Specimen 184); in order to obtain maximum corrosion resistance, it is important that the solutions of Steps B, C and D of this example be slightly basic or near ³³ basic as possible. In this connection it is to be mentioned that the titrated solution of MgAc2 was used for Specimen 190 and the freshly made solution for Specimen 189 for the time period of the corrosion resistance test of the modified coating gave the same results. Further ⁶⁰ to he noted is that the KAc (Specimen 192) gave the same results as MgAc₂ (Specimens 190 and 191).

Based on titrations of the NaOH activating solutions and the Procedure C solutions for Specimens 184-186 and 188-191 (both before and after use), it was noted ⁶³ that in treating these specimens, these solutions became more acid. In this connection note Example 6.

With reference to Procedures B and C of this example, after using the respective solution (those given or solutions used in place thereof), the pH should be adjusted ⁷θ to bring it back to the pH of a freshly made solution, by, for example, adding NaOH, in order to obtain best results (also see Examples 6 and 15). However if the same solutions are used many times with readjustment of pH, it is to be understood that additional solute will ⁷³ have to be added since the concentration thereof is re3,374.155 duced where the same solution is reused to treat additional specimens.

EXAMPLE 15

In order to determine the effect of reusing a solution, Specimens 193 and 194 were treated the same as Specimens 190 and 191 of the preceding example other than as noted.

posed to each individual solution, including an activating solution, separately (contrast Specimens 196 and 197). However the corrosion resistance of Specimen 197 is good and was substantially increased so that it will be 5 ample for many purposes.

EXAMPLE 17

TABLE 31

Specimen Diflerence Time Results _____________ (hrs.)

193..-....... Used solution of MgAcs of 190 which was first brought back to original alkalinity by adding NaOH.

No attack.

All the specimens of this example were a 3003 alloy and were pretreated as set forth in the first sentence of 10 Example 8.

The subsequent treatment comprised subjecting the respective specimens to one or more Of the following solutions for the time and temperature indicated below.

194.........KAc of solution 191 brought back to original acidity and then 5 cc. 1% of NaOH added to one liter of solution.

8 small pits one side;

very small and 5 small pits along scratch on other side.

No attack.

Concentration

Temperature (a) KOH, .32gms./liter...._____________ (b) NaOH, .32 gms./liter_________________ (c) NiAcs+FeNH-i Citrate (4.9 gms, each/liter).

(d) FeNHiCgOi, 9.8 gms./liter____

Boiling____________

-----do_____________

160° J?_____________ plus 200° but not

Time (min.)

1 small pit one side;

no attack on other.

This shows that the acetate solutions may be reused if the alkalinity is controlled and still obtain very good results.

_z boiling.

(e) Do____________________________________do...— (^f) J'eNHiCsOi, 9.8 gms./liter plus added____Ido

NaOH until turned alkaline.

(g) NajCaOa NaOH added to H2C2O4 do until slightly alkaline.

(h) KAc, .32 gms./liter plus per gal. of_____do______ solution, 5 cc. of 1% NaOH/2 liters was added.

(i) NaOH, .32 gms./liter__________.___________.do (j) Kassil #1 (28 cc./liter)—do2””_—

EXAMPLE 16

All the specimens of this example were a 3003 alloy and. were successively subjected to a 1-minute sulfuric acid electrolyte, a 15-second caustic etch, rinsed in water, a 45-minute sulfuric acid electrolyte and rinsed in water’ The subsequent treatment comprised subjecting the respective specimen to one or more of the following solutions for the time and temperature indicated. The various solutions used were as follows:

Concentration

Temperature

Time (mi:i.) ³⁰

The solutions used and the results of the NaOH corrosion test are given below in Table 33.

TABLE 33

Specimen A B G D Time Results (hrs.)

199....- a d

200...—— b e

201_________ b e (a) NaOH (.45 gms./liter)_________________Boiling (b) NiAc3+*FeNH4C (4.9 gins. each/ 160° - -- ---- liter).

(0) (9.8 gms. KAo+,13 gms. NaOH)/ 200° but not liter. boiling (d) (9.8 gms. KAo+,32 gms. NaOH)/ do liter.

$ ------------------------------Boiling------------W Do..............„............ d₀ (g) (9.8 gms. MgAc₂+.13 gms. NaOH)/ 200° but not.......

liter. boiling (h) Kassil #1 .(28 cc./liter).do-„

202-..-....- a ci

203--------- b ci

204--..- bf

205.....—_ b g

206--------- b h

The solutions used in treating the various specimens and the results of the NaOH corrosion test are given below in Table 32.

No attack.

No attack one side, 3 fairly large areas attacked on other side.

No attack.

No attack one side, other 1 fairly large and 3 smaller areas attacked.

No attack.

No attack one side, very large area attacked on other.

No attack, removed from test.

Do.

No attack.

1¼ Severe attack.

No attack.

No attack one side, 2 very small pits on other.

No attack.

Medium attack in scratch and 1 small pit one side; other attack in 3 small scratches and 1 small pit on other.

_______________ TABLE 32 ’ ’Specimen A B C D Time Results (hrs.)

195-------- ϊ b g h

196------ a c h

197.——... e .... h

198--—... a d h

No attack.

Only slight edge attack.

No attack.

Do.

3 pits one side, numerous pits on the bottom.

One corner attacked on one side, attack along edge and top of other side, numerous small pits.

The appearance of Specimen 197 after the corrosion test was similar to that obtained when all the electrolyte solution had not been removed prior to further treatment, while the attack on Specimen 198 appeared similar to that where the concentration of NaOH of the activating step was too high or the exposure too long. It is to be noted that combining the NaOH with the acetate solution in an attempt to minimize the number of different solutions that a specimen is treated with does not give as good results as where the specimen is successively exAs may be noted, KOH can be substituted for NaOH in the activating step and still obtain the same results. 55 That is the NaOH and KOH solutions worked best for activating the previously produced aluminum oxide coating. However a too strongly alkaline solution, see Specimens 82-85 (Example 7), and Specimens 94, 95, 97 (Example -8-), apparently does overly-severely attack the 60 aluminum oxide coating and thereby prevents obtaining maximum corrosion resistance in accordance with this invention. Of course it is to be understood that with a stronger alkaline solution, a short time of treatment and/or a lower temperature would provide a degree Of 65 compensation for not having used a less basic activating solution.

In substituting FeNH₄C₂O₄, which is very acid, in Step B of this example, Specimen 204 was severely attacked at 1½ hours but not at 1 hour. This shows ferric ammo70 nium oxalate together with the activating and silicate steps does increase corrosion resistance when compared to only aluminum oxide coated specimens. The effects of acidity of this oxalite could not be overcome by heating the treated Specimens 199 and 200 in the solution of 75 NaOH used per Step C for these specimens. Further mak3,374,155 ing the ferric ammonium oxalate alkaline precipitated the iron and did not impart the desired corrosion resistance (see Specimen 204). It was noted after the respective oxalate treatment, Specimen 204 was a deep red; whereas for the acid oxalate, Specimens 199, 200 and 201 were a golden color. The aforegoing is in contrast to using sodium oxalate which was made by adding sodium hydroxide to oxalic acid until the resulting solution was slightly alkaline; and which imparted very good corrosion resistance, see Specimen 205.

From the above examples it is to be noted that by activating the chemically or electrolytically formed aluminum oxide coating with an inorganic base, provided the concentration, time and temperature are such that the oxide coating is not severely attacked; and a subsequent silicate treatment, the corrosion resistance is substantially enhanced. The corrosion resistance is substantially additionally enhanced by interjecting a treatment between the activating step and the silicate treatment step that comprises subjecting the specimen to an organic compound of a metal which deposits an oxide in the aluminum oxide coating. However as appears above, optimum results are not obtained if such a compound is more than slightly acid. That is, if such a compound is more than slightly acid and cannot be made nearly neutral or somewhat basic by adding, for example, NaOH, without precipitation, the said interjected treatment will produce adverse results. It is preferred that the pH of the solutions of Procedures B and in particular that of nickel acetate and ferric ammonium citrate be about a pH of 5.3-6. Additionally, in order to obtain best results the article being coated with the modified oxide of this invention should preferably have all the natural oxide coating cleaned off, for example, used in a rolled condition, subject to a good etch and/or buff clean.

It is considered that the activation step and the silicate treatment steps are the two most important steps of this invention in modifying an aluminum oxide coating regardless of chemically or anodically formed. Additionally to maximize the corrosion resistance a precipitate or an oxide of a heavy metal such as indicated in Procedure B and a precipitate of an oxide of an alkali or alkali earth metal of Procedure C should be included in the modified coating, the solutions utilized in forming these precipitates preferably being slightly basic or as close to being basic as practical without causing the solute to precipitate in the solution.

EXAMPLE 18

To determine the effects of adding an oxidizing agent (nitric acid) to the solutions of Procedures B and C four specimens of 5457 alloy were treated. Specimens 208 and 210 were degreased, caustic etched for one minute, treated to a bright dip and subjected to a sulfuric acid electrolyte for 40 minutes, while Specimens 207 and 209 were degreased and then subjected to a sulfuric acid electrolyte for 40 minutes without any intermediate treatment. Each of these specimens were treated in a NaOH (15 gms./ liter) for 10 minutes at 120°-140° F. and treated to the one or more of the solutions as set forth in Table 34 under Procedures B and C and finally to solution (e) before the corrosion test. The various solutions used are as follows:

<td> Solution Time</td><td> Temperature er.)</td>

<td> (a) NiAcs+FeNHiAci (4.5 gms. each/liter). 15 min----</td><td> 120-140</td>

<td> (b) NiAcs+FeNHiAci (4.5 gms. each/liter). 15 min---- +1 cc. cone. HNOa/liter.</td><td> „ 120-140</td>

<td> (c) MgAc₃ (8.9 gms./liter)___________________30 min---- (d) MgAcs (8.9 gms./liter4-l cc. cone. HNO₃/liter).</td><td> 212</td>

<td> (e) Liquid G’.T.W. (28 cc./liter)____________1 hr-------</td><td> — 212</td>

TABLE 34

Procedure Procedure Elapsed Corrosion Test Results

Specimen B C Time (hrs.)

207_________ a c

208_________ b c

209_________ a d

210_________ b d

No attack.

Small pits one side, considerable attack in scratches and numerous pits on other.

3¼ No attack.

Very slight attack.

Numerous small pits one side, other numerous small pits in area that appeared like fingerprint.

3½ Considerable attack.

Considerable attack on both sides.

3½ Some attack.

Do.

Considerable attack on both sides.

As may be noted, the addition of nitric acid decreases the resistance to corrosion. This is consistent with the remarks made under Example 6.

EXAMPLE 19

A series of specimens were subjected to an anodic treatment for 45 minutes at 72° F., the alloy and the electrolyte being indicated in Table 35. After the anodic treatment the specimens were water rinsed, air dried and 30 wrapped in Kimpak paper. A few days later, the specimens were successively treated in the solutions as follows:

NaOH (.32 gms./liter)______________________30 min......Bolling.

KAc (9.8 gms.fliter)________________________30 min------ 200-212° F.

Kassil #1 (28 cc./liter)_______________________30 min------ 200-212° F.

------------------------------------------------------- and then subjected to the corrosion test. The results are given below in Table 35.

For these specimens one of the following electrolyte ₄₀ solutions was used, the particular solution for a given specimen being indicated in Table 35:

(a) 15% H₂SO₄+5% chromic acid, (b) 15% H₂SO₄+10% molybdic acid, (c) 15% H2SO₄-|-hydrazine sulfate.

.- TABLE 35

<td colspan="2"> Specimen</td><td> Alloy</td><td> Electrolyte</td><td> Elasped Time (hrs.)</td><td> Corrision Test Results</td>

<td> 50</td><td> 211_________</td><td> 3003</td><td> c</td><td> 3½ 3¾</td><td> Only attack in scratche both sides. Severe attack on both sides.</td>

<td> 55</td><td> 212_________</td><td> 5357</td><td> b</td><td> 7¾ 15</td><td> Both sides attack in scratches, some pitting on polished side. Severe attack on unpolished side; attack in scratches and along bottom of polished side, large area not attacked.</td>

<td> 60</td><td> 213_________</td><td> 5357</td><td> c</td><td> 7¾ 15</td><td> Attack in scratches of both sides, slight pitting on polished side. Moderate attack in scratches on unpolished side, attack in 2 scratches and few scattered pits which started at defects on polished side.</td>

<td> 65</td><td> 214-________</td><td> 3003</td><td> a</td><td> 4 8</td><td> No attack. Unpolished side had severe attack on sides and bottom and small pits in central area; polished side had moderate attack on sides and bottom and few small pits tn central area.</td>

<td> 70 75</td><td> 215_________</td><td> 3003</td><td> c</td><td> 4 8</td><td> No attack. Unpolished side had severe attack on sides, bottom and inner area; polished side had moderate attack on sides and bottom, few few small pits in central area.</td>

3,374,155

It. is believed that the severity of the attack of the specimens of Table 35 was largely due to the washing and drying procedure at the end of the anodic treatment since the specimens were stored with adjacent planar surfaces abutting one another. Thus if the specimens were not completely rinsed and dried, during storage the water would seep to the side and bottom edges and thereby cause a condition that gave the above results. It is believed that upon further investigation, the use of hydrazine sulfate and similar compounds in the electrolyte will give better results than those indicated to date.

Although the tests for corrosion resistance given above are indicated by the resistance to a 1% NaOH solution, it is to be understood the modified coatings of this invention also resist acid attack. This is shown in the Example 20 as follows:

EXAMPLE 20

Specimens 216-224 inclusive which were alloy 3003 were first degreased, flash sulfuric acid electrolyte treated, rinsed in water, subjected to a 20-second caustic etch’ rinsed in water, dipped in acid to remove smudge, rinsed in water, then subjected to a 40-minute sulfuric acid electrolyte and then thoroughly rinsed with water. Specimens 216, 220, 223 and 224 were then subjected to the treatment of Steps (e), (f), (g) and (h) for Table 15 of Example 5; while Specimens 218 and 219 were then subjected to the treatment of Steps (e) and (h) for Table 15 of Example 5 and Specimens 217, 221 and 222 were then - ^(k.Lw^{li,0H (7}·^{5 co}· ®oⁿo-fi-)+Dequest only given a boiling water seal for 15 minutes. The thus treated specimens were rinsed with water and exposed to the corrosion medium as given in the Table 36.

TABLE 36 trolyte for 45 minutes; while Specimen 425, an 1100 alloy, was subjected to a 1% caustic etch and a sulfuric acid electrolyte for 45 minutes; and Specimen 426, an 1100 alloy was subjected to a 1% caustic etch, a 30 second bright dip and a sulfuric acid electrolyte for 45 minutes Each of Specimens 422-432, and 428α were then rinsed in water, next successively treated to two or more of the solutions of Table 37 as indicated in Table 38 and finally to a 1.0% NaOH corrosion test. The results of the test are given in Table 38.

With reference to Table 37, where the concentration for NaOH is indicated in “cc.,” this means the solution used required the given number of cc, of 0.1 NHC1 to neutralize a 25 cc. of the NaOH solution which for solutions (g), (h) it indicates the cc. of 0.1 HC1 to neutralize a 5 cc. sample.

____________ TABLE 37

Solution Time Temperature

15min------Boiling.

min Do.

min Do.

mln. Do.

30min.._._. 200-212° F.

min______ 200-212° F.

min______ 200-212° F.

min______ 200-212° F' min______ 200-212° F.

mln......Boiling.

min______ 200-212° F.

min______ 200-212° F.

min______ 200-212° F.

(a) NaOH (.3gms./liter)...... .

(b) NaOH (1.6 cc.).....

(c) NaOH (2.10cc.).

^liter’^{5 C}°' ^COn°' ^NH,0H+·^{3 gms}· NaOH)/ (e) Kassil #1 (27cc./liter)...................

(Q ® gms.+NaOH, 1.35 gms.)7i___ (g) NH4OH (4.80 cc.)..;._ (h) ΝΗ,ΟΗ (2.60 cc.)___ (i) ..(NHd,Cp₃ (9.0 gms./l.)+NaOH (Π” gms./l.).

(j) . Solution (1) with 7.5 co. cone. NH4OH ’ added.

2006 -------—1 (m) NH4OH ¢7.9 cc. conc./l.)____ (n) (NH₄)₂ OOs (9.8 gms./l.)+NH₁O’H (4 ee. conc./l.).

Specimen Corrosion Medium Time Results

1% NaOH, room temp. 16 hrs_____No attack.

... 4 hrs...... Attack in scratches on each side.

16hrs_.._. Above attack biit more severe, medium pitting on both sides.

min-----Severe attack.

hrs-----No attack.

..44 hrs_____ Do.

.. 16 hrs.....Noticeable attack.

hrs_____Considerable attack, some coating still on

220,224------ 1% oxalic acid, 212° F_. 11 min—_ No noticeable attack.

min.... Some gas being liberated at surface.

45min_._. Noticeable attack but not all coating dissolved.

2¼ min... Coating dissolved.

As may be noted for Specimens 220, 222 and 224 the oxalic acid was at about boiling in order to increase the speed of the attack since at room temperature the corrosion test oxalic acid solution did not attack the coating as rapidly as the corrosion test sodium hydroxide solution.

EXAMPLE 21

It has been found that various compounds that release ammonia in an aqueous solution during the time that aluminum specimens are immersed therein enhances the resistance to corrosion. It is preferred that such ammonium compounds be applied as a Procedure B step, however, as may be noted hereinafter, an ammonium compound advantageously be used in a basic aqueous solution in the Procedure A step (see Example 26—Specimen 463). Illustrative of the manner of treatment and the very good results obtained are shown by Specimen 400 of Example 2 and Specimens 422-432 below.

Specimens 422—432 and 428α were first degreased and then pretreated as follows: Specimens 422, 423, 427-429, 428α, 431 and 432 which were a 3003 alloy, were successively subjected to a 5-minute dilute caustic etch, and a sulfuric acid electrolyte for 45 minutes; while Specimen 424 was subjected to a 5% caustic etch for 1 minute, a 1% caustic etch for 3 minutes and a sulfuric acid elec216.

218.

217.

223 _

219.

221.

222.

.do _____do..:____________

1% oxalic acid, room temp.

-----do______________

-----do______________ .do

Specimen

422.

423.

424.—

425,426.

427_____

428_____

428a.

429.

430.

431. .432.

b c a a

TABLE 38

BCD Elapsed Corrosion test Results time (hrs.) 20 27 e e e e e

e e e

24 48 20 20

17

12

No attack.

No attack one side, 2 very small pits on other.

small pits one side, 2 very small pits on other.

no attack.

Do.

small pit each side.

No attack.

Do.

Do.

No attack one side, 1 very small pit other.

Same as 17 hrs.

No attack.

No attack one side, large area of attack on other.

No attack.

Uniform attack.

No attack.

Do.

Do.

Slight attack in scratches one side, pitting starting on other.

To be noted is Specimen 429 wherein the solution for Procedure A contained NaOH, (NH₄)₂₁CO₃ and NH_t0H which shows that a basic solution using a compound that releases ammonia in solution together with NaOH in the same solution gives good results, as well as other specimens where such an ammonium compound were used only in the Procedure B solution. Further Specimens 422-432, 428α show that very good results can be obtained by eliminating the Procedure C treatment if the aforementioned type of ammonium compound is used. Also attention is directed to Specimens 428, 428α of Example 21 where ammonium carbonate is used.

EXAMPLE 22

The specimens of this example are primarily directed to show the use of various ammonium compounds in the Procedure B step. All these specimens were given a pretreatment that included degreasing a caustic etch, a 45minute sulfuric acid electrolyte treatment, and rinsed in

3,374,155 water. The subsequent treatment comprised subjecting the respective specimens to two or more of the following solutions for the time and temperature indicated.

Concentration Time Temperature (min.)

5

15 15 30

15

30

30

Boiling. 200-212° F. Boiling.

Do.

200-212° F. Do. Do.

Do. Do.

Do. Do.

Do.

Do.

Do. Do.

(a) NaOH, .3 gms./liter---------------------- (b) Kassil #1 (27 cc.fliter)--------------------- (c) NaOH, .3 gms./liter----------------------- (d) Do____________________________________ (e) ‘NHiCnO- (5.3 gms./liter)----------------- (f)« iNH* HPO, (5.3 gms.Alter)„ (g) NH1 CI (5.3 gms./liter)+NaOH (.16 gms./ liter). „, (h) ΝΗ,ΟΗ (7.9 cc. conc./liter)(1) NH, trartrate (9.8 gms./liter) + 12.1 cc. of 1% NaOH/liter.

(i)· (NH,)₂ oxalate (5.3 gms./liter)------------(k) NH,Ac (required 0.6 cc. .1NHC1 to neutralize 25 cc. sample).

(m) *NHiC (9 gms./liter, same solution as for specimen 401).

(n) 'NH&lt;C (9 gms./liter, same solution as for specimen 402).

(ο) NH,Ac (cone, of solution (k))------------(p) KAc--------------------------------—--Note—(1) Solutions e, f, j, were made alkaline by the addition of 1.3 cc. of concentrated NH4OH per liter. (2) Specimen 441 pretreated the same as Specimens 446,447.

The solutions used and the results of the NaOH corrosion test are given below in Table 39.

Comparing Specimens 401, 442 with specimens such as 443, 402 it was noted Specimens 401, 442 gave better results, although, up to 17 hours there was no appreciable difference. The type of treatment for Specimens 443, 402 indicated that too much of the coating was removed by the KAc treatment.

The results from the specimens of this example and other examples indicate that combining the ammonium compounds with the NaOH of Procedure A does not give as good results where the ammonium compounds are used in a solution separate and after the Procedure A treatment with NaOH (without the ammonium compounds); although with both types of treatment, the corrosion resistance was substantially enhanced over that without the treatment of this invention.

It has also been found that making solutions such as ammonium tartrate and ammonium oxalate basic with NH₄0H gave better results than those made basic with NaOH. Also, of the ammonia compounds, using NH₄OH after the activation treatment gave better results than other ammonia compounds that have been tried. With reference to the above, also see Example 27. From other runs it has been noted that NH₄ tartrate gives better results than (NH^aSOafNHajaMoO^ while (NH₄)₂CO₃

TABLE 39

Procedure

Specimen Alloy ----------—

433.......... 3003 a e ...... b

434.......... 3003 a f ...... b

435.......... 3003 a g ...... b

436.......... 3003 c h ...... b

437.......... 3003 d h ------ b

438.......... 3003 d h ...... b

439.................... a 1 ...... b

440..............—a j ...... b

Elapsed

Time Corrosion Test Results (hrs.)

Slight attack in 4 scratches on one side, none other.

Slight attack in numerous scratches one side, none other.

¼ Increased attack in scratches one side, none other.

Increased attack in scratches one side, 4 fine pits other.

Increased attack in scratches one side, numerous small pits.

No attack one side, slight attack in scratches one side and bottom on other.

Slight attack in scratches on both sides and on bottom of other.

4½ Same as 3 hrs. plus 2 areas of pitting on other.

Slight attack in scratches one side, considerable attack in scratches and pitting on other.

Slight attack in scratches on side, none other.

Same as 2 hrs. plus 2 long scratches on one side.

4½ Increased attack in scratches on one side, none other.

Increased attack in scratches on one side, 5 pits other.

Increased attack in scratches on one side, 7 pits other.

No attack.

1 small pit and attack in scratches at bottom on one side, 4 small pits other.

Few small pits and attack in scratches at bottom one side, 4 small pits and 3 very small pits on other.

A number of small pits one side, increased size of pits on other.

No attack.

Few small pits one side, no attack other.

Few small pits both sides.

Increased attack in pits.

No attack one side, 2 amall pits other.

Same as 3 hrs.

Few small pits both sides.

Pits increased in size.

1½ No attack.

6½ Attack in scratches and pitting one side, no attack other.

Considerable attack in scratches and medium pitting one side, a medium number of pits other.

No attack.

Numerous small pits one side, no attack other.

Increased attack in pits one side, pits along bottom, few in scratches, plus five pits on other.

3,374,155

Table 39—Continued

Specimen Alloy —---—— ---- Timo Corrosion Test Results ~ -a- u jd (hrs.)

441---------- 3003 a k ______ b

442...------- 3003 a m ______ b

43---------- 3003 a n p b

444-------------------- _a o p b

Increased attack over 7 hrs. as given above.

1¾ No attack one side, only attack in scratches near bottom on other.

5½ Few small pits one side, numerous small pits and attack in scratches near bottom on other.

Same as 5½ hrs.

9½ Medium pitting one side, same as 7 hrs. on other.

No attack.

9½ 2 small pits, one side, small pits along edge on other.

Same as 9½ hrs.

Few more small pits one side, small pits along edge ot other.

14½ No attack.

Medium attack large area on side, none other.

5¼ No attack.

No attack one side, attack In scratches.

9½ Number of small pits one side, some pitting and attack In scratches on other.

Medium number of pits one side, medium pits and attack in scratches other.

and NH₄ citrate gave better results than the NH₄ tartrate; and (NH₄)₂HPO₄ and NH₄ oxalate gave better results than (NH₄)₂SO₄ and (NH₄)₂MoO₄ but not as good as NH₄ citrate.

EXAMPLE 23

The specimens of this example are primarily directed to the effec^ of varying the time of treatment in an amπιοηΪΗ’ solution. Each of the specimens were pretreated including a 45-minute sulfuric electrolyte treatment and successively treated to the solutions as follows:

Solution Time Tempera___________

-------------— See Table 40_____Boiling, (b) NH4OH.................. 200-212° F (c) Kassil #1 (27 cc./liter of water).......ao-min 200-212° F*

The time of treatment in solutions (a) and (b), the concentration of solution (b) and the corrosion test results are given below in Table 40.

TABLE 40

<td rowspan="2"> Specimen </td><td colspan="2"> Time (min.)</td><td rowspan="2"> Elapsed - Time, (hrs.)</td><td rowspan="2"> Corrosion Test Results</td>

<td> Sol. A</td><td> Sol. B</td>

<td> 445_________</td><td> 3</td><td> 5</td><td> 3 4' 5</td><td> No attack. Attack on bottom edge one side,, slight attack in scratches on other. General attack.</td>

<td> 446_______...</td><td> 15</td><td> 5</td><td> 2 3</td><td> No attack. General attack with numerous small pits.</td>

<td> 447.........</td><td> 15</td><td> 20</td><td> 13 16</td><td> No attack. 12 small pits one side, 25 small pits and row of pits in scratches other.</td>

<td> 448_________</td><td> 15</td><td> 30</td><td> 11 13 16</td><td> Slight attack in scratch one side, no attack other. Same as 11 hrs. except addition of 5 small pits in scratch on said one side. Attack increased on one side, a number of medium sized pits other.</td>

Note.—(1) Concentration of (b) solution for Specimens 445, 446 5 cc sample required 3.8 cc. of 0.1 N HC1 to. neutralize. (2) Concentration of xt ^{ior s}P^ecimens 447, 448, 5 cc. sample required 4.45 cc. of 0 1 in HGl to neutralize.

Also to be noted is Specimen . 432, Example 21 which was immersed in a NH₄0H solution for 15 minutes. As may be noted from Specimens 432 an 1 447 very good results are obtained successively using NaOH for 15 minutes, NH₄OH for 15-20 minutes and Kassil #1 for 30 minutes; and. are very nearly the same as obtained with the successive NaOH NiAc₃+FeNH₄ citrate, MgAc₂ or 30 KAc, and Kassil #1 treatments. An advantage of the

NaOH, NH₄OH, Kassil #1 treatment is; that the concentrations of solutions used are easier to control and adjust. This is also true where ammonium carbonate made alkaline with NH₄OH is substituted for NH₄OH in Procedure B.

EXAMPLE 24

A group of specimens, Specimens 449-453, were treated to determine the effect of varying the temperature of treatment in a NH₄OH solution. These specimens were first degreased, etched 2 minutes in 5% caustic, 3 minutes in 2% caustic, subjected to a sulfuric acid electrolyte treatment for 45 minutes, rinsed with water and successively treated to the solution as follows:

________ Solution ______ Time_____ Temperature fM NTTrnif···----------------15 min------------Boiling.

---------------JSmjn------------See table 41.

(c) Kassil #1-------------------- 30 min____________ 200-212° F.

<td colspan="2"> The temperature of the NH₄0H solutions and the time 50 and results of the corrosion tests are given in Table 41.</td>

<td></td><td> TABLE 41</td>

<td> Specimen Temp. NHiOH</td><td> Elapsed Corrosion Test Results Time, hrs.</td>

<td> 449-----------Room Temp... 55</td><td> 3 Attack in scratches near bottom one side, no attack other side. 5 Same as 3 hrs. plus a few pits on said one side. 6 Same as 5 hrs. plus numer- ous pits on said one side. 10 Same as 6 hrs. plus some</td>

<td> 60 450--------.. 140-170° F_______</td><td> pits on said other side. 4 No attack. 5 Slight attack in scratches</td>

<td rowspan="2"> 451______... 200-212° F....... 65</td><td> both sides...... 10 Same as 5 hrs. plus a few pits bothsides.</td>

<td> 5 No attack. 6 2 small pits one side, slight attack in scratches on otherside. 10 Both sides slight attack in scratches, a few pits on other.</td>

<td> 452 --------- 200-212° F_______</td><td> 8 No attack. 17 A number of small pits one side, considerable numbers</td>

<td> 70 453__________ 250° F.___________</td><td> of small pits on other. 17 No attack. 20 A few small pits one side.</td>

The results indicate that satisfactory improved results can be obtained using ammonium compounds for the Pro75 cedure B step at room temperature,, that desirable results:

3,374,155

44 are obtained with a temperature range of 140-250° F., and that it is preferred that the temperature be 200250° F.

EXAMPLE 25

The specimens of this example are primarily directed to the effects of varying the concentration of the NH₄OH solution in the Procedure B step, these specimens being pretreated in the same manner set forth for the specimens of Example 24 and these successively treated to the solutions as follows:

The specimens were then tested in a 1% NaOH solution, the results of the test being given below.

<td colspan="4"> TABLE 42</td>

<td> Specimen</td><td> Concentration of Solution b</td><td> Time Elapsed, (hrs.)</td><td> Corrosion Test Results</td>

<td> 454_________</td><td> .53 cc. concen trated/liter.</td><td> 4 6 10</td><td> No attack one side, a fewsmall pits other side. Same as 4 hrs. plus slight attack in scratches on other. Attack in scratches and few pits one side, a few small pits and attack in a large number of scratches.</td>

<td> 455.........</td><td rowspan="2"> 1.06____________</td><td> 4</td><td> No attack.</td>

<td></td><td> 5 6 10</td><td> No attack one side, a few small pits on other. Same as 5 hrs. Slight attack in scratches one side, pits increased, in size and number on other.</td>

<td rowspan="2"> 456.........</td><td rowspan="2"> . 2.1-.......—-</td><td> 4</td><td> No attack one side, a few</td>

<td> 5 5 10</td><td> small pits other. 2 small pits and slight attack in scratches one side, a few small pits on other. 7 pits and slight attack in scratches one side, increase in size and number of pits on other.</td>

<td rowspan="2"> 457_________</td><td rowspan="2"> 5.3_____________</td><td> 4</td><td> No attack.</td>

<td> 5 10</td><td> 1 small pit each side. Same as 5 hrs.</td>

<td> 458-.-.....</td><td> . 7.9_____________</td><td> 3 4 5 10</td><td> Pits in defect near bottom one side, no attack other. Same as 3 hrs. plus slight attack in scratches on said one side. Same as 4 hrs. for said one side, 2 pits in scratch on other. Deep pits in defect and considerable attack in scratches on one side,</td>

<td></td><td></td><td></td><td> attack in scratches and a number of pits near edge on other.</td>

<td> 459----:.</td><td> . 15.8____________</td><td> 1 3 4 8¼</td><td> Attack in scratches near edges one side, no attack other side. Attack in scratches near edges and some pits one side, attack in number of scratches and few pits on other. Same as 3 hrs. plus few pits on said other side. Severe attack in scratches and pits both sides.</td>

The lower concentrations of NH₄0H gave the best results, i.e., 0.5 cc. to 5.0 cc. of concentrated NH₄OH per liter of water. However improved results are obtained over a relatively large range of concentrations of NH₄0H.

EXAMPLE 26

Specimens 460-462 were pretreated the same as the specimens of Example 24 while Specimens 463, 464 were pretreated the same except the etch was a 4-minute dilute caustic etch. Specimens 460-464 were then successively treated m two or more of the solutions indicated in

<td colspan="3"> Table 43, the results of the corrosion tests also being given in Table 43. The various solutions are as follows:</td>

<td> 5</td><td colspan="2"> (a) NaOH (.3 gros./liter)____________________ 15 mln------Boiling. (b) NaOH (.08 gms./liter) - —........ 15 min------ Do. (0) NaOH (.16 gms./liter)___________________15 mm------ Do. (d) (NaOH, .3 gms.-f-NHiOH, 7.5 cc. 30 min------ Do. (θ)°*ΝΗΛθ(9 gms./liter)____________________15 min------ 200-212° F. (f) NHiOH (7.9 co. conc./litor)______________15 min------ 200-212 F. (g) Kassil #1 (14 cc./liter)-------------------30 min------ 200-212 F. (h) Kassil #1 (28 cc./liter)___________________30 mln------ 200-212 F.</td>

<td> 10</td><td></td><td> TABLE 43</td>

<td></td><td colspan="2"> Procedure Time Specimen ---------------—----- Elapsed, Results A B C D (hrs.)</td>

<td> 15 20 25 30 35</td><td> 460_________ a f .. 461_________ b £ - 462......... c f . 463 _ d .......</td><td> g 2 No attack. 3 Slight attack in scratches one side, none other. 5 Slight attack in scratches one side, a few small pits other. 8¼ Considerable attack in scratches and number of pits one side, few small pits other. h 1 Attack in scratches one side, pitting in numerous areas on other. 2 Same as 1 hr. plus pitting on one side and attack in scratches on other. 3 Same as 2 hrs. except pitting severe on both sides. 4 Same as 2 hrs. except very severe pitting both sides. ..... h 3 No attack. 4 3 small pits one side, 2 small pits other. 5 3 small pits one side, 7 small pits other. 8 Several small pits one side, 7 small pits and attack in scratch on other. ..... h 17 No attack.</td>

<td> 40</td><td> 464_________ d e .</td><td> 18 Attack one small scratch one side, one small pit other. 19 Same as 18 hrs. _____ h 17 No attack. 18 No attack one side, slight attack in scratches on other. 20 Same as 18 hrs.</td>

<td> 45 50 55</td><td colspan="2"> Comparing Specimen 460 with Specimen 458 of the preceding example where only the concentration of Kassil #1 was varied, it is noted that the higher concentration of Kassil #1 gives better results. Likewise comparing Specimens 461 and 462 where only the concentration of NaOH was varied, the high concentration of NaOH gave better results. With reference to Specimens 463, 464, NH4OH was added to the activating solution of Procedure A and gives good results. However in order to obtain more consistent results, it is preferred that the ammonium compound used be in the solution of the Procedure B step rather than the Procedure A step.</td>

<td colspan="2"></td><td> EXAMPLE 27</td>

<td> 65</td><td colspan="2"> Each of Specimens 465-473 were pretreated successively as set forth in Table 44, then subjected to a 45minute sulfuric acid electrolyte treatment and then rinsed except for Specimen 472 which was, after the sulfuric ; acid electrolytic treatment, immersed in concentrated HNO3 acid for 15 minutes and then rinsed.</td>

<td></td><td></td><td> TABLE 44</td>

<td></td><td> Specimen Alloy</td><td> Pretreatment</td>

<td colspan="2"> 465..... - 3003 466,467.._____ 3003 468..................... 469,470,471--. 1100 472,473...... 1100 75 -----------------</td><td> Etched 1 min. in 5% caustic, etched 3 min. in 1% caustic. Etched 2 min. in 5% caustic, immersed 2 min. in cone. HF acid. Etched in 1% caustic. Do. 2 mim caustic etch, immersed 2 min, in 15% HiSOj’acid.</td>

Each of Specimens Procedure A solution

3,374,155

4θ

465-473 inclusive was treated to a in terms of cc. of 0.1 N HC1 of NaOH for 15 minutes (other cc. sample.

required to neutralize a 25

TABLE 45

Solution Time

Specimen Cone. A Cone. B ConclT Corrosion Test Results

465---------- 1.8 3.8 ........

466---------- 1.35 2.0 4.7

467---------- 1.35 1.75 _________

468---------- 1.95 3.25 2.85

469----------- 2.25 3.30 _________

--------- 2.25 1.65 ............

471---------- 2.25 4.90 ________.....

472---------- 2.05 3.85 2.85

473-.------ 2.5 3.85 2.8

No attack.

N o attack one side, large area of coating dissolved on other.

No attack.

No attack one side, slight attack in one area on other.

Area of attack one side, large area of severe attack on other.

No attack.

No attack one side, area of general attack on other.

No attack.

No attack one side, slight attack at bottom edge of other.

Same as 6 hrs.

No attack one side, 1 very small pit other.

Same as 6 hrs.

Same as 6 hrs plus light attack in scratch on other side.

1 large area of severe attack each side, severe attack in scratches on other.

Very severe attack large area one side, several large areas and scratches severely attacked on ot her.

No attack one side, 2 light scratches and a few very small pits other.

Same as 6 hrs.

Pits bottom edge one side, other same as 6 hrs.

Pew small pits one side, increased attack in pits and scratches plus new areas of attack on other.

Numerous small pits one side, other same as 18 hrs.

No attack.

2 light scratches attack one side, no attack other.

Same as 7hrs. plus 3 small pits on said one side.

Same as 7 hrs. on said one side, light scratch attacked on other.

Increased attack in 2 light scratches and 3 small pits one side, attack in 1 light scratch on other.

Same as 18 hrs.

No attack.

No attack one side, 1 pit and scratch other.

Same as 17 hrs.

No attack.

No attack one side, 1 slight scratch and 1 pit other.

No attack one side, severe attack in large area of pits other.

atanSm up iron and than specimen 472 which was for 8 minutes) at boiling, the concentration of the. NaOH being set forth in Table 45 as the number of cc. of 0.1 NHC1 required to neutralize a 25 cc. sample of the Procedure A solution. Each of Specimens 465-469, 472 and 473 were then treated to a Pro- θο cedure B solution of NH₄OH for 15 minutes at 200-212° ' F., the concentration of the Procedure B solution being set forth in Table 45 as the number of cc. of 0..1 NHC1 required to neutralize a 5 cc. sample of the solution. The Procedure B solution for specimens 470 was 9.8 gms. of 65 NH₄ citrate plus 7.9 cc. one percent NaOH per liter of water while the Procedure B solution for Specimen 471 was 2.6 cc. concentrated NH₄OH plus 2.6 cc. of Dequest per liter of water, the treatment being for 15 minutes at 200-212° F. for each of Specimens 470, 471. After the Procedure B treatment, each of Specimens. 465-473 was subjected to a Procedure D treatment of Kassil #1 at boiling, Specimens. 465-470, 472^; and. 473 being for 30 minutes and Specimen 471 for 20 minutes. The-alkalinity of some of the Procedure D solutions is given iri Table 45

With reference to Specimens 472, 473, immersing the etched specimens in H₂SO₄ for a short period of time before the electrolyte treatment is advantageous in that it does a better job of removing smudges which tend to interfere with providing a good corrosion resistance coating.

COMMENTS (1) From various tests it was noted that treating specimens in a freshly made solution of Procedures A, B C and D respectively did not give as good results as solutions that were reused with adjustment to restore alkalinity where necessary. Thus it is preferred that the solutions be “broken in” (aluminum dissolved in the solution) before forming the oxide coating of this invention 70 on aluminum articles.

(2) Also it has been noted that using specimens having initial surface defects, such as scratches, that are treated in accordance with this invention are usually initially attacked in the defect. That is, frequently in the NaOH 75 corrosion test the first noticeable attack is in the defect,

3,374,155 tions used being approximately the same as a freshly made aqueous solution of the respective compound used.

2. The process of claim 1 further characterized in that the pH of the nickel acetate, ferric ammonium citrate is about 5.5-8.

3. In the method of forming a coating on an aluminum article to increase the corrosive resistance of the article, prior to artifically producing an oxide coating on the article, subjecting the article to a dilute caustic, etch and then to a non-electrolyzing sulfuric acid solution for a few minutes; thence artifically producing an aluminum oxide coating on said article; thereafter subjecting said article to an aqueous solution of an inorganic base of about .15-1.1 grams solute per liter for about 5-30 minutes at a temperature in the range of about room temperature to 250° F. and of an effective composition that a non-overly severely attacked aluminum oxide coating remains on said article at the end of the aforementioned period; and subsequently treating said article in an alkaline solution of a silicate selected from the group consisting of sodium silicate and potassium silicate of a concentration of about 14 cc. to 112 cc. per liter of water for a period of a minimum of about 15 minutes at about 200° to 250° F.

4. In the method of forming a coating on an aluminum article to increase the corrosive resistance of the article, artificially producing an aluminum oxide coating on said article, the step of artificially producing an oxide coating comprising electrolyzing a solution containing sulfuric 30 acid, thereafter subjecting said article to an aqueous solution of an inorganic base of 0.2-0.55 gram solute per liter for about 5-30 minutes at a temperature in the range of about room temperature to 250° F. of an effective composition that a non-overly severely attacked alumi35 num oxide coating remains on the article at the end of the aforementioned period; and subsequently treating said article in an alkaline solution of a silicate selected from the group consisting of sodium silicate and potassium silicate of a concentration of about 14 cc. to 112 cc. per and therefore it is preferred that the article to be coated be as free from defects as is reasonably possible. However the modified coating of this invention substantially improves the corrosion resistance even in specimens that were observed to have surface defects prior to treatment. Also it has been noted that relatively early edge attack results from the shearing operation to produce the specimens, improper shearing apparently causing small cracks in the edges of the metal.

(3) With reference to the various specimens treated with ammonium compounds, those that during the treatment step which more noticeably gave off ammonia (sensed by smell) produced better results than those which did not. For example using a NH₄ citrate solution without the addition of a base such as NaOH or KOH did not give as good results as those that had such a base added. The addition of a base appeared to more readily release ammonia during the treatment and thus it is expected that it would be advantageous in the Procedure B step to bubble NH₃ gas through the solution during the treatment. The addition of NaOH or KOH apparently frees NH₄0H over a longer period of time. However as previously indicated, an overly alkaline solution is to be avoided as the coating previously on the specimen is overly attacked.

(4) Results indicate that to obtain best resistance to corrosion, the Procedure A treatment should be at least 10-15 minutes while a further increase to 30 minutes does not provide much increase over 15 minutes.

(5) To be avoided is placing a specimen that has been subjected to an electrolytic treatment in a highly oxidizing acid such as concentrated nitric acid or hydrofluoric acid before the Procedure A treatment. Also to be avoided is placing the specimens in an oxidizing solution after the caustic etch and before the electrolytic treatment.

(6) With reference to the treatments of Procedures B and C, it is preferred that the solutions used be not more than weakly acid and that such solutions be in the pH range of 6.5 to 8.0. Also it is preferred that the treatment ------------- . . .__. , ,, between the Procedure A and the Procedure D treatment ⁴⁰ liter of water for^a^penod o£ a minimum of about 1 include subjecting the aluminum article to an aqueous solution having a solute selected organic alkali metallic compounds, organic earth metallic compounds, organic iron group compounds, and an ammonium compounds that release ammonium hydroxide in solution in a quantity noticeable by smell where the aforementioned compounds have an anion selected from the group of acetates, citrates, carbonates, oxalates and tartrates, and ammonium hydroxide.

As many widely apparently different embodiments of 50 this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments herein.