DE102009016111A1 - Hypereutectic aluminum-silicon casting alloy and process for its processing in die casting - Google Patents

Abstract

A die-cast body made of a hypereutectic aluminum-silicon casting alloy with more than 15 to 25 wt .-% silicon, 0.005 to 0.3 wt .-% zirconium and a total of 0 to 10 wt .-% of other fog alloying components and ad 100 wt % Aluminum is produced by a die casting process so that the precipitation of the primary silicon takes place only in the casting mold. This is achieved by a content in the alloy of calcium and / or strontium of each element or in total from 0.001 to less than 0.05 wt .-%, wherein the content of phosphorus is less than 0.002 wt .-% and the content of carbon less than 0.0007 wt .-% is set. The invention reduces mold wear.

Description

The The invention relates to a hypereutectic aluminum-silicon casting alloy with more than 15 to 25 wt .-% silicon and a total of 0 to 10% by weight of minor constituents and ad 100% by weight of aluminum, a process for producing a die-cast hypereutectic Aluminum-silicon alloy with calcium and / or strontium addition and a wear-resistant product of the invention Alloy and a process for its production, which is the process-safe and cost-effective production of wear-stressed Aluminum castings in diecasting possible.

Recently, the use of hypereutectic aluminum-silicon alloys for wear-stressed components, such as cylinder crankcases, pistons, pumps, compressor housings, propellers has increased significantly. The good wear resistance of these alloys is based on the presence of primary silicon precipitates in the structure, which should be present in an advantageous and homogeneous as possible size distribution and geometric shape. In order to achieve this, a refining of the primary silicon with phosphorus has proved successful, which produces nuclei in the melt, at which point the primary silicon crystals are formed ( Foundry 78, 1991, No. 23, pp. 848-852 ).

From the EP 1 683 881 A1 For example, an improved Al-Si alloy having 6 to 22 weight percent Si, which was developed for die casting processes, is known. To reduce tack, the strontium content in this alloy is in the range of 0.05 to 0.2 wt%. However, a disadvantage is that the in the patent EP 1 683 881 A1 Strontium levels indicated cause an undesirable change in the morphology of the primary silicon from polyhedral to star-shaped. The further consequences are a noticeable coarsening of the primary silicon crystals and a significant decrease in the volume fraction of this hard phase in the microstructure.

The currently required high casting temperature for hypereutectic Al-Si alloys from 760 ° C to 800 ° C leads noticeable decrease in the viscosity of the melt and increases significantly the risk of spewing out of the mold. this will additionally by the high released heat of crystallization favored in the excretion of primary silicon crystals. The promoted by higher temperatures oxidation and hydrogen uptake result beyond that for the 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, the abrasive effect is enhanced the primary silicon particles on the casting tools and thus significantly reduces their service life. All these factors set the limits for processing the hypereutectic Al-Si alloys downcasting by die casting.

Of the Invention is based on the object, an alloy and a method to provide a process-reliable and cost-effective production of wear-stressed aluminum castings in die casting allows.

These The object is achieved by the features of claim 1, namely by targeted Adjustment of calcium and / or strontium in the hypereutectic Al-Si alloys in effective amounts from 0.001 (≥ 0.001) % By weight to less than 0.05 (<0.05) Wt .-%, preferably to <0.04 Wt .-%, more preferably to <0.03 Wt .-%.

The Alloy according to the invention is one with the main components aluminum and silicon, more precisely with silicon contents from> 15% by weight to ≦ 25 Wt .-%, and zirconium as a minor constituent in one Amount of 0.005 to 0.3 wt .-%. It is a hypereutectic Alloy. The sum of the secondary alloy constituents should thereby Not exceed 18 wt .-% and preferably 10 wt .-%.

Especially advantageous die-cast alloys are obtained when the Silicon content above 16 wt .-%, and more preferably about 18% by weight.

For the invention is essential that the phosphorus content in the alloy is limited to a few ppm. It has been found that precisely the avoidance of phosphorus and the use of calcium or else strontium or a combination of the elements Ca and Sr brings about the desired effects. Phosphorus additives increase the crystallization temperature of the primary silicon, which inevitably leads to higher casting temperatures and higher precipitation temperatures of the abrasive primary silicon particles. The high mold wear with conventional hypereutectic Al-Si die cast alloys can therefore be attributed to the addition of phosphorus. According to the invention, therefore, the content of phosphorus is kept less than 0.002 wt .-% (20 ppm). Preferably, the phosphorus content does not exceed 10 ppm and more preferably 2 not 9 ppm, more preferably not 7 ppm.

Further It was found that it is essential that the carbon content as low as possible. By not completely pure starting materials entrained carbon degraded the casting results. The carbon content should therefore be in the alloy according to the invention less than 0.0007 % By weight.

The results of the inventors show that the refining and formation of the primary silicon in alloys according to the invention is markedly improved by zirconium additions of 0.005 to 0.3% by weight, without increasing the precipitation temperature of the primary silicon crystals. This is because the Si ₂ Zr particles formed after Zr addition in the melt are less patent than AIP nuclei and require significant supercooling to be ineffective.

The According to the invention provided treatment of hypereutectic Aluminum-silicon melt by addition of calcium or Strontium in effective amounts added causes a significant decrease the excretion temperature of the primary silicon and makes It is possible the casting temperatures of hypereutectic Al-Si alloys significantly compared to the prior art to reduce. Low casting temperatures and accordingly ensure higher viscosity of the melt a low-risk processing of die casting without Danger of spitting out. Additional benefits are the lower thermal load of the casting tools and considerable Increase their service life. The mold wear becomes clear reduced. Furthermore, the shift ensures the excretion temperature of the primary silicon at a later date, that this hard phase arises only in the die, so that the long-known abrasive effect of the hard Primary silicon crystals on the casting tools deleted in the new process.

The achieved with the method according to the invention smaller Solidification interval of hypereutectic Al-Si alloys also contributes to the significant improvement their warm cracking behavior, which is particularly in the production from monolithic engine blocks in die casting because of their elaborate ribbing is of great benefit.

It it has been found that a clacium Strontium addition an excellent structure modification brings with it. The essential features of the structure modification are a significant refining and homogeneous distribution of the primary silicon particles and at the same time a good finishing of the Al-Si eutectic. there are the primary silicon crystals in the structure in the desired polyhedral shape. The long time aimed at combined refining of the primary and Refinement of the Al-Si eutectic is known to be guaranteed the best wear resistance and lead to Improvement of mechanical properties.

In principle, suitable secondary alloy elements for aluminum-silicon alloys which are to be further processed by die casting into technical components are known to the person skilled in the art. The minor alloying components impart special properties to the alloy which are essential for usability. In development of the invention are provided as possible secondary alloy components:
0 to 6% by weight of copper (Cu),
0 to 1% by weight of magnesium (Mg),
0 to 2% by weight of iron (Fe),
0 to 3 wt .-% nickel (Ni),
0 to 0.3% by weight of chromium (Cr),
0 to 1 wt .-% manganese (Mn),
0 to 3% by weight of zinc (Zn),
0 to 0.5% by weight of cobalt (Co),
0 to 0.3% by weight of titanium (Ti),
0 to 0.1% by weight boron (B),
0 to 0.1% by weight of vanadium (V).

From These components can be added one or more become.

At Contaminant elements should not exceed 0.6% by weight in total present in the alloy to have uncontrollable effects to exclude the properties of the alloy. In this case, impurity elements are, in particular, Sn, Pb, Bi and Sb. Particular care should be taken that the antimony content is below 0.01 Wt .-% is because higher levels the effect of Ca and Sr impair.

Preferably, in the microstructure of the alloy according to the invention are primary silicon crystals in vorwie polyhedral form present. Star-shaped primary silicon crystals should not be present or only in small quantities.

Farther it is preferred that the primary silicon crystals in the microstructure a mean diameter (= (maximum expansion of the particle + minimum dimension of the particle) / 2) of 50 μm, preferably 20 microns, more preferably 10 microns and especially preferably not exceed 7 microns, or on average do not exceed.

The The invention further comprises a method for producing a Die-cast hypereutectic aluminum-silicon alloy with calcium and / or strontium addition.

The The object of the invention is therefore also achieved by a Process for producing a die-cast body, in which a hypereutectic Al-Si alloy containing Calcium and / or strontium of each element or in total from 0.001 to less than 0.05 wt .-% (≥ 0.001 to <0.05 wt .-%), a content of phosphorus less than 0.002 wt .-% and a content of carbon smaller as 0.0007 wt% with mold fill times of 10 to 300 milliseconds is processed by die casting, the excretion of the primary silicon first done in the mold.

ever According to silicon content, the temperature of the melt in the casting chamber approx. between 670 ° C and 700 ° C.

The hypereutectic Al-Si alloys with silicon contents of more than 15 or 16 or 18 wt .-% are characterized by wide solidification intervals out. Therefore, they require short mold filling times and rapid pressure build-up at mold filling to premature To avoid solidification and to achieve maximum pore compression.

The exact composition of the hypereutectic Al-Si alloy is preferred as described above.

In Further development of the invention, the calcium in the form of a calcium master alloy and / or the strontium is added in the form of a strontium master alloy is used, in particular AlCa10, AlSr90 and AlSr10 become.

Even though already in the casting state good mechanical values can exist made of the alloy of the invention Castings are subjected to all heat treatments. In Further development of the invention is therefore provided that the diecasting after casting a heat treatment, a mechanical Processing, a honing operation or a combination of several Undergoing treatments.

The Casting skin of the alloy according to the invention can due to rapid solidification in the die casting process on primary silicon to be impoverished. Therefore, the primary silicon depleted Edge zone to be removed. This can be z. B. by mechanical processing or by honing operation.

The The object of the invention is finally solved by a wear-resistant product, which with a inventive Die casting process is made. In the wear-resistant Product is generally 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, a Engine block, or generally a machine or device part.

Under Referring to the figures, the invention is by way of example to be explained in more detail without the invention would be limited to this example.

1 shows a discharged by die casting test specimen;

2 shows the cooling curves of an alloy AlSi17Cu4Mg with 50 ppm phosphorus and an AlSi17Cu4Mg alloy according to the invention with 70 ppm calcium;

3 shows the microstructure of an alloy according to the invention AlSi17Cu4Mg with the addition of 70 ppm calcium, × 500.

example

Representing the large group of hypereutectic Al-Si cast alloys, AlSi17Cu4Mg alloys were selected. The test alloys with calcium and with phosphorus were produced in an electrically heated crucible furnace. The addition of calcium successes using the commercial master AlCa10 alloy. The addition of phosphorus to the comparative alloy was carried out with wire master alloy AlCu20P1,4. The casting tests were carried out on the GDK 750 die casting machine (Müller Weingarten (Germany)) with a casting speed of 50 m / s. The casting temperature was 700 ° C and the mold temperature was 180 ° C. The properly discharged with the inventive method test specimen is in 1 shown.

Table 1 shows the composition of the alloys investigated. Table 1. Composition of Al-Si Cast Alloys, wt% Si Ca P Cu Ni mg Fe Mn Cr Ti Zr Req. Leg. 16.5 0,007 0.0009 3.7 0.02 0.6 0.18 0.14 0.03 0.07 0.005 Leg. according to the prior art 16.5 0.0009 0.005 3.9 0.03 0.6 0.16 0.16 0.04 0.05 -

2 represents the casting technology advantages of the method according to the invention over the prior art convincing. The lowering of the excretion temperature of the primary silicon by 27 ° C by treatment of the melt with 70 ppm of calcium is clearly visible.

In the microstructure of the casting cast off with the new method, a good finishing and a good fine-tuning of the primary silicon (7 μm) was achieved at the same time. 3 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1683881 A1 [0003, 0003]

Cited non-patent literature

• Foundry 78, 1991, No. 23, pp. 848-852 [0002]

Claims (10)

Hypereutectic aluminum-silicon casting alloy with more than 15 up to 25% by weight of silicon, 0.005 to 0.3% by weight Zirconium and with a total of 0 to 10 wt .-% of other secondary alloying constituents and ad 100 wt .-% aluminum, characterized by a content of calcium and / or strontium of each element or in total from 0.001 to less than 0.05 wt .-%, wherein the content of phosphorus is less than 0.002 wt% and the content of carbon is less than 0.0007 wt% is. Hypereutectic aluminum-silicon casting alloy according to claim 1, characterized in that as secondary alloying ingredient at least one of the following elements is present in the alloy is: 0 to 6% by weight of copper (Cu), 0 to 1 wt .-% magnesium (Mg), 0 to 2% by weight of iron (Fe), 0 to 3 wt .-% nickel (Ni) 0 to 0.3% by weight of chromium (Cr), 0 to 1 wt .-% manganese (Mn), 0 to 3% by weight of zinc (Zn), 0 to 0.5 wt .-% cobalt (Co) 0 to 0.3% by weight of titanium (Ti), 0 to 0.1% by weight boron (B), 0 to 0.1% by weight of vanadium (V). Hypereutectic aluminum-silicon casting alloy according to claim 1 or 2, characterized in that impurity elements in total, in a content of not more than 0.6% by weight in the alloy available. Hypereutectic aluminum-silicon casting alloy according to one of claims 1 to 3, characterized that the primary silicon crystals in the structure one average diameter of 50 microns. Hypereutectic aluminum-silicon casting alloy according to one of claims 1 to 4, characterized that in the structure primary silicon crystals in polyhedral Form are present. Method for producing a diecast body, characterized in that a hypereutectic 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 .-%, a content of phosphorus less than 0.002 wt .-% and a content of carbon smaller as 0.0007 wt% with mold fill times of 10 to 300 milliseconds is processed by die casting, the excretion of the primary silicon first done in the mold. Method according to Claim 6, characterized that an alloy composition according to any one of claims 1 to 5 is used. Method according to claim 6 or 7, characterized that the calcium in the form of a calcium master alloy and / or the Strontium added in the form of a strontium master alloy is used, in particular AlCa10, AlSr90 and AlSr10 become. Method according to one of claims 6 to 8, characterized in that the diecasting after casting a heat treatment, a mechanical treatment or is subjected to a honing operation. Wear-resistant product, manufactured with a method according to any one of claims 6 to 9, characterized characterized in that it is 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, a Engine block, a machine or equipment part.