Pressure casting mould made of a hypereutectic aluminium silicon cast alloy and method for producing same

p0001The invention relates to a die-cast body made of a hypereutectic aluminum-silicon casting alloy with more than 15 up to 25 wt .-% silicon and with a total of 0 to 10 wt .-% of by-alloy components, and ad 100 wt .-% aluminum, a process for producing a die-cast body made of this alloy, the calcium and / or strontium the manufacturing method ermöglichtdie process reliable and cost-effective production of wear-stressed aluminum castings in die casting.

p0002Lately, the use of hypereutectic aluminum-silicon alloys for wear-exposed components such as engine blocks, pistons, pumps, compressor housing, propeller has increased significantly. The good wear resistance of these alloys is due to the presence of primary silicon precipitates in the structure, which should be in an advantageous and homogenous size distribution and geometrical shape. To achieve this, a refining of primary silicon has proved with phosphorus, which produces in the melt nuclei on which arise, the primary silicon crystals (<nplcit id="ncit0001" npl-type="s"><text>Foundry 78, 1991, no. 23, pp 848-852</text></nplcit>).

p0003From the <patcit id="pcit0001" dnum="EP1683881A1"><text>EP 1683881 A1</text></patcit> is an improved Al-Si alloy containing 6 to 22 wt .-% Si known which has been developed for die casting. To reduce the tendency of the strontium content in this alloy in the range of 0.05 to 0.2 wt .-% before. A disadvantage of, however, that the patent<patcit id="pcit0002" dnum="EP1683881A1"><text>EP 1683881 A1</text></patcit> given strontium contents undesired change in the morphology of primary silicon of polyhedral to star-shaped rise. The further consequences are a noticeable coarsening of primary silicon crystals and a significant decrease in the volume fraction of the hard phase in the microstructure.

p0004From the <patcit id="pcit0003" dnum="EP1978120A1"><text>EP 1978120 A1</text></patcit> discloses an aluminum-silicon casting alloy with a selectively adjusted, low carbon content from 0.0007 to 0.1 wt .-%. This alloy has good ductility combined with low susceptibility to corrosion.

p0005The currently required high casting temperature for hyper-eutectic Al-Si alloys of 760 ° C to 800 ° C resulting in noticeable decrease in the viscosity of the melt and significantly increases the risk of spouting from the mold. This is additionally promoted by the high liberated crystallization heat in the elimination of primary silicon crystals. Encouraged by higher temperatures oxidation and hydrogen absorption lead moreover to increased formation of oxide inclusions and porosities. The relatively high crystallization temperature of the primary silicon in known aluminum-silicon casting alloys for die casting enhances the abrasive effect of the molding tools and reduces Primärsiliziumteilchen to thus considerably their service life. All these factors set the limits for the processing of the hypereutectic Al-Si alloys with the die casting down.

p0006The invention has for its object to provide an alloy and a method which enables a process-safe and cost-effective production of wear-stressed aluminum castings in die casting.

p0007This object is achieved by the features of claim 1, namely through targeted recruitment of calcium and / or strontium in the hypereutectic Al-Si alloys in effective amounts of from 0.001 (≥0,001) wt .-% to less than 0.05 ( &lt;0.05) wt .-%, preferably to &lt;0.04 wt .-%, more preferably to &lt;0.03 wt .-%.

p0008The die-cast body of the invention is one having the main alloying components of aluminum and silicon, or more precisely with silicon contents of> 15 wt .-% to? 25 wt .-%, and zirconium as a by-alloy component in an amount of 0.005 to 0.3 wt .-%. This is a hyper-eutectic alloy. The sum of the secondary alloy components should not exceed 18 wt .-% and preferably 10 wt .-%.

p0009Particularly advantageous diecasting alloys are obtained when the silicon content of over 16 wt .-.% And more preferably more than 18 wt .-% is.

p0010For the invention it is essential that the phosphorus content is limited in the alloy to a few ppm. It has been found that it is the avoidance of the use of phosphorus and calcium, or strontium, or a combination of the elements Ca and Sr provides the desired effects. Phosphorus additives increase the crystallization temperature of the primary silicon, resulting inevitably higher casting temperatures and higher precipitation temperatures of abrasive silicon primary leads. The high mold wear with conventional hypereutectic Al-Si-diecasting alloys can therefore be attributed to the addition of phosphorus. According to the invention the content of phosphorus (20 ppm) is therefore smaller than 0.002 wt .-% retained. Preferably, the phosphorus content does not exceed 10 ppm and more preferably not 9 ppm, more preferably not 7 ppm.

p0011Further, it was found that it is essential that the carbon content is as low as possible. By not completely pure starting materials of introduced carbon deteriorates the casting results. The carbon content should therefore be in the alloy of the invention is less than 0.0007 wt .-%.

p0012The results of the inventors show that the refining and training form of primary silicon in die-cast alloys of the invention by Zirkoniumzusätze from 0.005 to 0.3 wt .-% is significantly improved, without increasing the precipitation temperature of the primary silicon crystals. This is because that formed in the melt by adding Zr Si2Zr particles are less patent than AIP germs and need a marked hypothermia to be keinmwirksam.

p0013The inventively provided treatment of hyper-eutectic aluminum-silicon melt by the addition of calcium or strontium in effective amounts of addition causes a substantial decrease in precipitation temperature of the primary silicon and makes it possible to use the casting temperatures of hypereutectic Al-Si alloys as compared to the prior art clearly to reduce. Low casting temperatures and correspondingly higher viscosity of the melt to ensure a low-risk handling of the die casting process without risk of spouting. Additional advantages are the lower thermal load of the casting tools and substantial increase of their service life. The form of wear is significantly reduced. Furthermore, the shift of the precipitation temperature of the primary silicon for later ensures that these hard phase is formed only in the die, so that the long-known abrasive action of hard primary silicon crystals attributable to the molding tools in the new process. The obtained by the method according to the invention smaller solidification range of the hypereutectic Al-Si alloys also contributes significantly to improve its hot cracking behavior, which is particularly in the production of monolithic engine blocks in the diecasting because of their elaborate ribbing of great advantage.

p0014It has been found that the calcium or strontium addition invention brings an excellent structural modification with themselves. The essential features of the structure modification are a significant refining and homogeneous distribution of Primärsiliziumteilchen and simultaneously a good modification of Al-Si eutectic. The primary silicon crystals are present in the desired polyhedral shape in the structure. The long awaited combined refining of Primärslilziums and Veredeltung the Al-Si eutectic ensure the best known, wear resistance and lead to improved mechanical properties.

p0015Basically, the skilled worker are suitable by alloying elements for aluminum-silicon alloys, which are to be further processed in the die casting to technical components known. Adverse alloy components give the alloy special features that are essential for the fitness for use. In development of the invention are provided as a possible side alloy components:<ul><li>0 to 6 wt .-% copper (Cu),</li><li>0 to 1 wt .-% Magnesium (Mg),</li><li>0 to 2 wt .-% of iron (Fe),</li><li>0 to 3 wt .-% of nickel (Ni),</li><li>0 to 0.3 wt .-% of chromium (Cr),</li><li>0 to 1 wt .-% of manganese (Mn),</li><li>0 to 3 wt .-% of zinc (Zn),</li><li>0 to 0.5 wt .-% of cobalt (Co),</li><li>0 to 0.3 wt .-% of titanium (Ti),</li><li>0 to 0.1 wt .-% of boron (B),</li><li>0 to 0.1 wt .-% of vanadium (V).</li></ul>

p0016Of these components one or more may be added.

p0017An impurity elements in total should be available wt .-% in the alloy to exclude uncontrollable effects on the properties of the alloy can not be more than 0.6. Impurity elements are here in particular Sn, Pb, Bi and Sb. Particularly is to pay attention that the antimony content below 0.01 wt .-% is because higher levels impair the effect of Ca and Sr.

p0018Preferably, in the structure of die-cast body according to the invention primary silicon crystals in polyhedral form predominantly present. Star-shaped primary silicon crystals should be present or only in small quantities.

p0019Furthermore, it is preferred that the primary silicon crystals in the structure have an average diameter (= (maximum dimension of the particle + minimum extension of the particle) / 2) of 50 microns, preferably 20 microns, more preferably 10 microns and more preferably not exceed 7 microns, or not exceed the average.

p0020The invention further comprises a method for preparing a processable in the pressure cast hypereutectic aluminum-silicon alloy with calcium and / or strontium addition.

p0021The object of the invention is therefore also achieved by a method for producing a die-cast body in which a hyper-eutectic Al-Si alloy with a content of calcium and / or strontium of each element, or in total from 0.001 to less than 0.05 wt % (? 0.001 to &lt;0.05 wt .-%) is processed, a content of phosphorus is less than 0.002 .-% and a content of carbon is less than 0.0007 wt wt .-% with Formfüllzeiten of 10 to 300 milliseconds in the diecast is, the elimination of the primary silicon takes place only in the mold.

p0022Depending on the silicon content, the temperature of the melt in the casting chamber approximately between 670 ° C and 700 ° C may be.

p0023The hypereutectic Al-Si alloys with silicon contents of more than 15 or 16 or 18 wt .-% are characterized by broad solidification intervals. Therefore, they need short Formfüllzeiten and rapid pressure build-up in the form filling to prevent premature solidification and to achieve maximum pore compaction.

p0024The exact composition of the hypereutectic Al-Si alloy is preferably as described above.

p0025In development of the invention, the calcium in the form of a calcium alloy and / or strontium is added in the form of a strontium master alloy, which implies in particular AlCa10, AlSr90 and AlSr10 be used.

p0026Although as cast good mechanical values ​​exist, all heat treatments may be subjected from the invention alloy produced castings. In development of the invention is therefore provided that the pressure casting after casting a heat treatment, a mechanical treatment, a honing operation, or a combination of several treatments is subjected.

p0027The casting skin of the inventive alloy can be depleted by rapid solidification the pressure casting of primary silicon. Therefore, the depleted silicon primary edge zone can be removed. This can be done by mechanical treatment or by honing operation z. B..

p0028The object of the invention is finally also achieved by the use of a wear resistant product namely a manufactured with die-casting process of the invention pressure casting for a technical component, in particular a piston, a cylinder crankcase, a liner, a propeller, a propeller blade, a pump, a pump housing , a compressor housing, an engine block, or generally a machine or apparatus part.

p0029With reference to the figures, the invention is an example to be explained in more detail, without the invention being limited to this example.<dl id="dl0001"><dt>Fig. 1</dt><dd>showing a drained in diecasting specimen;</dd><dt>FIG. 2</dt><dd>shows the cooling curves of an alloy AlSi17Cu4Mg with 50 ppm phosphorus and an inventive alloy AlSi17Cu4Mg with 70 ppm calcium;</dd><dt>Fig. 3</dt><dd>shows the microstructure of an alloy according to the invention AlSi17Cu4Mg with the addition of 70 ppm calcium, x 500th</dd></dl>

example

p0030Representing the large group of hypereutectic Al-Si casting alloys, the alloys of the group AlSi17Cu4Mg were selected. The experimental alloys with calcium and phosphorus were prepared in an electrically heated crucible furnace. The addition of calcium page using the standard alloy AlCa10. The addition of phosphorus to the comparative alloy was carried out with wire alloy AlCu20P1,4. The casting tests 750 (Fa. Müller Weingarten (Germany)) at a casting speed of 50 m / s were carried out at the die casting machine GDK. The casting temperature was 700 ° C and the mold temperature was 180 ° C. The properly decanted with the inventive specimen is in<figref idrefs="f0001">Fig. 1</figref> shown.

p0031Table 1 shows the composition of the alloys tested.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1. Composition of the Al-Si casting alloys, wt .-%</title><tgroup cols="12"><colspec colnum="1" colname="col1" colwidth="37mm" /><colspec colnum="2" colname="col2" colwidth="12mm" /><colspec colnum="3" colname="col3" colwidth="15mm" /><colspec colnum="4" colname="col4" colwidth="15mm" /><colspec colnum="5" colname="col5" colwidth="10mm" /><colspec colnum="6" colname="col6" colwidth="12mm" /><colspec colnum="7" colname="col7" colwidth="10mm" /><colspec colnum="8" colname="col8" colwidth="12mm" /><colspec colnum="9" colname="col9" colwidth="12mm" /><colspec colnum="10" colname="col10" colwidth="12mm" /><colspec colnum="11" colname="col11" colwidth="12mm" /><colspec colnum="12" colname="col12" colwidth="13mm" /><thead><row><entry valign="top" /><entry valign="top">Si</entry><entry valign="top">Ca</entry><entry valign="top">P</entry><entry valign="top">Cu</entry><entry valign="top">Ni</entry><entry valign="top">Mg</entry><entry valign="top">Fe</entry><entry valign="top">Mn</entry><entry valign="top">Cr</entry><entry valign="top">Ti</entry><entry valign="top">Zr</entry></row></thead><tbody><row><entry>Erf.Leg</entry><entry>16.5</entry><entry>0,007</entry><entry>0.0009</entry><entry>3.7</entry><entry>0.02</entry><entry>0.6</entry><entry>0.18</entry><entry>0.14</entry><entry>0.03</entry><entry>0.07</entry><entry>0.005</entry></row><row><entry>Leg. Gem. Art</entry><entry>16.5</entry><entry>0.0009</entry><entry>0.005</entry><entry>3.9</entry><entry>0.03</entry><entry>0.6</entry><entry>0.16</entry><entry>0.16</entry><entry>0.04</entry><entry>0.05</entry><entry>-</entry></row></tbody></tgroup></table></tables>

p0032<figref idrefs="f0001">FIG. 2</figref> represents the gießtechnologischen advantages of the method according to the invention over the prior art is convincing. The lower the precipitation temperature of the primary silicon to 27 ° C by treatment of the melt with 70 ppm of calcium can be seen clearly.

p0033In microstructure of the cast of the new methods alloy simultaneously a good finish and a good refining of primary silicon (7 microns) was achieved, <figref idrefs="f0002">Fig. 3</figref>,