EP1978120A1 - Aluminium-silicon alloy and method for production of same - Google Patents

Abstract

The main constituents are: aluminum 65 wt% or more, and silicon 5-25 wt%. Other components may also be present, together with inevitable impurities. The novel feature of the alloy is its carbon content of 0.0007 - 0.1 wt%. Up to 4 wt% of each of the following may be present, up to a total of 10 wt%: Mg, Mn, Fe, Co, Cu, Zn, Ni, V, Nb, Mo, Cr, T, Be, Pb, Li, Yt, Ce, Sc, Hf, Ag, Zr, Ti, Sr, Na, P, Ca, Sb, S, Ba, P, the remainder being at least 65 wt% aluminum, including inevitable impurities. The alloy especially contains 12.5 to 14.5 wt% silicon. In its microstructure, fine primary silicon and refined eutectic are simultaneously present. Intermetallic phases are also present as needles or small platelets up to 40 mu m in length. The carbon content is intentionally adjusted to 0.0007 to 0.1 wt%, by carbon addition in any form. The selected main components of the composition are melted, heating to a temperature in the range 720[deg] C -950[deg] C and poured into a mold. Carbon content is adjusted by addition of chemical compounds of carbon, and/or their mixtures, especially by addition of powdered carbides and carbo-nitrides, e.g. in the form of their sintered product. A carbon-containing aluminum pre-alloy is added into the melt of the normal constituents, or prior to melting them. An aluminum-titanium-carbon pre-alloy is used. In addition to carbon, the pre-alloy contains phosphorus. An independent claim IS INCLUDED FOR the method of manufacture.

Description

The invention relates to high and heat resistant silicon-containing aluminum casting alloys, their production and their use for the production of engine components.

To reduce emissions and fuel consumption as well as to increase the engine power in recent years, the combustion pressures and combustion temperatures of Binnstoffmotoren or combustion engines have increased, especially in the diesel engine. This led to increased demands on the thermo-mechanical loads for engine components.

In the state of the art, in particular in engine construction, Al casting alloys are known. Al castings are widely used because of their low specific weight, ease of molding and ease of processing. Also, through various casting methods, complicated workpieces such as e.g. Make pistons, cylinder heads, crankcases or engine blocks.

A proven alloy group for the production of engine components are Al-Si alloys. These materials are typically with silicon contents between 6 and 18 wt .-%, in some cases up to 24 wt .-% and with admixtures of magnesium from 1 to 1.5 wt .-%, copper between 1 and 4 wt .-% and often nickel between 1 to 3 wt .-% alloyed (catalog "aluminum casting alloys", VAW-IMCO).

In order to improve the heat resistance of the Al-Si alloys, for example, according to the US Pat. No. 6,419,769 B1 recommended to adjust the copper content between 5.6 and 8 wt .-%. However, in this case, the improvement of the mechanical strength is opposed to a deterioration in ductility, increase in specific gravity, and reduced corrosion resistance.

A heat resistant alloy with reduced specific gravity is used in the DE-PS 747 355 described as particularly advantageous for pistons. This material is characterized by a magnesium content between 4 and 12 wt.% And a silicon content between 0.5 and 5 wt .-% of. Furthermore, between 0.2 and 5 wt .-% copper and / or nickel may be alloyed. The high magnesium content leads to gas porosity due to the strong hydrogen absorption. The additional oxidation also involves the risk of oxide inclusions, which significantly degrade the mechanical properties of the casting.

In all of the abovementioned Al casting alloys, strength-enhancing Mg ₂ Si and Al ₂ Cu precipitates form via heat treatment, but these are not stable above 150 ° C. and therefore can not cope with the thermo-mechanical stresses of modern engines. By contrast, the intermetallic phases, such as Al ₆ Mn, Al ₃ Fe, Al ₇ Cr, Al ₃ Ni, Al ₈ Fe ₂ Si, Al ₇ Cu ₄ Ni, Al ₁₅ Mn ₃ Si ₂ , Al ₅ FeSi, Al ₃ Ti and Al ₃ Zr is unaffected by thermal long-term stress and, with favorable design (in quantity, size, shape and distribution), can make a considerable contribution to increasing the mechanical properties of the Al-Si alloys for engine construction. However, it is of particular importance that the homogeneous distribution and fine formation of the intermetallic phases in the cast structure is ensured in order not to impair the ductility of the alloy and its casting technology properties.

In the patent DE 101 17 298 C1 discloses a possibility for the texture modification of the Al-Si base alloy by addition of up to 3 wt .-% rare earths. The additions of rare earths cause a significant refining of the intermetallic phases, which results in a considerable improvement of the mechanical properties, in particular fatigue strength at elevated temperatures. However, the rare earths are very expensive and rarely used in practice.

The invention has for its object to provide a suitable alloy for the production of engine components, which has high strength, heat resistance, good creep strength and sufficient ductility with low susceptibility to corrosion and is also inexpensive.

This object is inventively by the selective adjustment of carbon in the Al-Si alloys in effective amounts of from 0.0007 to 0.1 wt .-%, preferably from 0.0007 to 0.05 wt .-%, more preferably 0.001 to 0.05 wt .-%, more preferably 0.001 to 0.01 wt .-%, more preferably 0.001 to 0.005 wt .-% dissolved.

• 5 bis 25 Gew.-% Silizium,
• 0,0007 bis 0,1 Gew.-% Kohlenstoff,
• jeweils 0 bis 4 Gew.-% der folgenden Legierungsbestandteile, wobei bevorzugt wenigstens einer dieser Bestandteile vorhanden ist und deren Summe bis 10 Gew.-%, vorzugsweise bis 6 Gew.-%, weiter vorzugsweise bis 4 Gew.-% beträgt:
  • Magnesium, Mangan, Eisen, Kobalt, Kupfer, Zink, Nickel, Vanadium, Niob,
  • Molybdän, Chrom, Wolfram, Beryllium, Blei, Lithium, Yttrium, Cer, Scandium, Hafnium, Silber, Zirkonium, Titan, Bor, Strontium, Natrium, Kalium, Calzium, Antimon, Schwefel, Barium, Phosphor,
• und als Rest auf 100 Gew.-% wenigstens 65 Gew.-% Aluminium einschließlich unvermeidbarer Verunreinigungen, wobei es sich insgesamt um eine Gusslegierung handeln soll.

The aluminum-silicon alloy according to the invention therefore has the following composition:

• 5 to 25% by weight of silicon,
• 0.0007 to 0.1% by weight of carbon,
• in each case 0 to 4% by weight of the following alloying constituents, preference being given to at least one of these constituents and the sum of which amounts to 10% by weight, preferably to 6% by weight, more preferably to 4% by weight:
  • Magnesium, manganese, iron, cobalt, copper, zinc, nickel, vanadium, niobium,
  • Molybdenum, chromium, tungsten, beryllium, lead, lithium, yttrium, cerium, scandium, hafnium, silver, zirconium, titanium, boron, strontium, sodium, potassium, calcium, antimony, sulfur, barium, phosphorus,
• and the remainder to 100% by weight of at least 65% by weight of aluminum including unavoidable impurities, all of which is a cast alloy.

Preferably, the aluminum-silicon casting alloy contains 5 to 18 wt .-%, in particular 12.5 to 14.5 wt .-% silicon.

• 0,1 bis 1,5 Gew.-%, insbesondere 0,1 bis 0,6 Gew.-% Magnesium;
• 0,001 bis 0,5 Gew.%, insbesondere 0,001 bis 0,3 Gew.-% Titan;
• 0,001 bis 0,7 Gew.-%, insbesondere 0,001 bis 0,4 Gew.-% Zirkonium;
• 0,001 bis 1,2 Gew.-%, insbesondere 0,001 bis 0,6 Gew.-% Mangan;
• 0,001 bis 2,5 Gew.-%, insbesondere 0,3 bis 0,8 Gew.-% Eisen;
• 0,001 bis 0,5 Gew.%, insbesondere 0,1 bis 0,4 Gew.-% Kobalt;
• 0,001 bis 0,5 Gew.-%, insbesondere 0,1 bis 0,4 Gew.-% Chrom;
• 0,0001 bis 0,1 Gew.-%, insbesondere 0,005 bis 0,01 Gew.-% Beryllium;
• 0,001 bis 2 Gew.-%, insbesondere 0,1 bis 1,5 Gew.-% Zink;
• 0,001 bis 4 Gew.-%, insbesondere 0,3 bis 1,8 Gew.-% Kupfer;
• 0,001 bis 4 Gew.-%, insbesondere 0,3 bis 3,0 Gew.-% Nickel;
• 0,001 bis 0,4 Gew.-%, insbesondere 0,05 bis 0,2 Gew.-% Vanadium;
• 0,0001 bis 1,2 Gew.-%, insbesondere 0,005 bis 0,5 Gew.-% Hafnium;
• 0,0001 bis 0,6 Gew.-%, insbesondere 0,005 bis 0,4 Gew.-% Niob;
• 0,0001 bis 0,4 Gew.-%, insbesondere 0,005 bis 0,2 Gew.-% Blei;
• 0,0001 bis 0,08 Gew.-%, insbesondere 0,005 bis 0,04 Gew.-% Strontium;
• 0,0001 bis 0,2 Gew.-%, insbesondere 0,002 bis 0,02 Gew.-% Natrium;
• 0,0001 bis 0,006 Gew.-%, insbesondere 0,002 bis 0,004 Gew.-% Calcium;
• 0,0001 bis 0,08 Gew.-%, insbesondere 0,01 bis 0,06 Gew.-% Bor;
• 0,0001 bis 0,4 Gew.-%, insbesondere 0,05 bis 0,3 Gew.-% Cer;
• 0,0001 bis 0,6 Gew.-%, insbesondere 0,05 bis 0,3 Gew.-% Scandium;
• 0,0001 bis 0,1 Gew.-%, insbesondere 0,001 bis 0,01 Gew.-% Phosphor.

Furthermore, it may be advantageous if further elements are present in the alloy, as indicated above. These are additives, which were added in comparison with aluminum and silicon in a minor amount. For example, the following amounts of additional alloying ingredients may be beneficial for the desired property profile:

• 0.1 to 1.5 wt .-%, in particular 0.1 to 0.6 wt .-% magnesium;
• 0.001 to 0.5% by weight, in particular 0.001 to 0.3% by weight, of titanium;
• 0.001 to 0.7% by weight, in particular 0.001 to 0.4% by weight, of zirconium;
• 0.001 to 1.2 wt .-%, in particular 0.001 to 0.6 wt .-% manganese;
• 0.001 to 2.5 wt .-%, in particular 0.3 to 0.8 wt .-% iron;
• 0.001 to 0.5% by weight, in particular 0.1 to 0.4% by weight of cobalt;
• 0.001 to 0.5 wt .-%, in particular 0.1 to 0.4 wt .-% chromium;
• 0.0001 to 0.1 wt .-%, in particular 0.005 to 0.01 wt .-% beryllium;
• 0.001 to 2 wt .-%, in particular 0.1 to 1.5 wt .-% zinc;
• 0.001 to 4 wt .-%, in particular 0.3 to 1.8 wt .-% copper;
• 0.001 to 4 wt .-%, in particular 0.3 to 3.0 wt .-% nickel;
• 0.001 to 0.4 wt .-%, in particular 0.05 to 0.2 wt .-% vanadium;
• 0.0001 to 1.2 wt .-%, in particular 0.005 to 0.5 wt .-% hafnium;
• 0.0001 to 0.6% by weight, especially 0.005 to 0.4% by weight of niobium;
• 0.0001 to 0.4 wt .-%, in particular 0.005 to 0.2 wt .-% lead;
• 0.0001 to 0.08 wt .-%, in particular 0.005 to 0.04 wt .-% strontium;
• 0.0001 to 0.2% by weight, especially 0.002 to 0.02% by weight of sodium;
• 0.0001 to 0.006 wt .-%, in particular 0.002 to 0.004 wt .-% calcium;
• 0.0001 to 0.08% by weight, in particular 0.01 to 0.06% by weight of boron;
• 0.0001 to 0.4% by weight, in particular 0.05 to 0.3% by weight of cerium;
• From 0.0001 to 0.6% by weight, in particular from 0.05 to 0.3% by weight of scandium;
• 0.0001 to 0.1 wt .-%, in particular 0.001 to 0.01 wt .-% phosphorus.

The aluminum-silicon casting alloy according to the invention is preferably characterized by the fact that in its microstructure fine primary silicon (less than 50 μm) and refined eutectic are present simultaneously, as can be seen from the micrograph. This condition is particularly desirable in near and hypereutectic Al-Si alloys.

The degree of finishing of the eutectic can be visually assessed by the foundry expert on the basis of the forms of formation of the eutectic silicon precipitates, for example with the aid of micrographs. For the visual assessment see also "foundry practice" No. 11/12 - 1993, page 206 - 209, G. Chai, L. Bäckerud, "Effective refining with strontium".

The modifying effect of the carbon on microstructures and properties of the Al-Si alloys was not known until the invention. It has been found that the carbon content according to the invention causes a change in the overall solidification behavior of the Al-Si casting alloys and brings about an excellent microstructure modification. As essential features of the structure modification by carbon are a considerable refining and homogeneous distribution of the intermetallic phases, a good refinement of the Al-Si eutectic and good refining of the primary silicon crystals. This results in a significant improvement of the mechanical and casting technology properties.

By adjusting the carbon content according to the invention, it is also possible to shift the concentration limits of important alloy components, such as titanium, zirconium, iron, manganese, chromium, cobalt, molybdenum and, depending on the application of other transition elements, to higher values without impairing alloy quality.

For example, in known Al-Si alloys with zirconium contents of more than 0.3% by weight, titanium contents of more than 0.3% by weight or iron contents of more than 0.6% by weight are formed in the microstructure very long acicular brittle phases.
The formation of these coarse intermetallic phases, as would be expected in the conventional aluminum alloys, ie especially long needles of intermetallic phases with transition elements such. Al3Zr, Al3Ti and Al5FeSi are suppressed by carbon. The very long acicular intermetallic phases typical for high contents of transition elements usually appear in the carbon-containing Al-Si alloys as "Chinese writing" or as small platelets up to a maximum of 30-40 μm in length. This brings significant benefits, such. As a significant improvement in the grain refining effect of the transition elements, as well as a significant increase in the mechanical properties, hot, creep and fatigue strength of the alloy of the invention. During casting, the melt shows a significantly improved mold filling and flow behavior, and the finished castings can be a significantly increased casting quality and in particular a significantly lower gas porosity can be detected.

In hypereutectic Al-Si alloys, the simultaneous refining of the primary silicon, the refining of the eutectic silicon and the smallest possible formation and homogeneous distribution of the intermetallic phases for setting the desired property profile is particularly important. This long-desired modification of the structure could not be achieved so far, since the effects of strontium and phosphorus cancel each other out. By Zulegieren the Near-eutectic and hypereutectic Al-Si alloys (especially for pistons and engine blocks) with the carbon and simultaneous addition of up to 100 ppm of phosphorus have achieved the desired combined microstructural influence.

For the processing of the alloy according to the invention, basically all casting methods are suitable. These include u. a. Sand casting, full mold casting, gravity die casting, low pressure die casting, differential die casting, die casting and vacuum die casting.

For the production of the aluminum-silicon casting alloy according to the invention, it is preferably provided that the basic constituents selected for the composition are melted together. The melting temperature is preferably from 650 ° C to 1000 ° C, more preferably from 720 ° C to 950 ° C. Then it is poured into a mold. "Melted together" also covers the gradual metering of all components into a common melt. Carbon can be used as elemental carbon, e.g. Graphite, but also be added in the form of a compound or master alloy.

According to a preferred embodiment, the carbon content is achieved in particular by adding chemical carbon compounds and / or their mixtures. This can also be done by adding powdered carbides and carbonitrides, also in the form of a sintered product of carbides and carbonitrides.

Alternatively, a carbonaceous aluminum master alloy may be incorporated into the melt from the remainder of the alloyed ingredients or may be added in advance to the components to be melted.

The carbonaceous additives can contain not only carbon but also phosphorus and / or nitrogen.

A particularly preferred method of this invention is to use an aluminum-titanium-carbon master alloy.

Although is out of the DE 37 29 937 A1 Already a grain refining with Al-Ti-C alloys known, but this refers expressly to Al-Ti main alloys. In doing so, long-known difficulties in increasing the carbon content of aluminum-titanium alloys are attributed to the difficulty in these compositions in achieving wetting between the carbon and the molten aluminum. The described master alloys are particularly useful in the production of thin sheet, films or can material.

Also, the addition of carbon-containing master alloys to pure aluminum and wrought aluminum alloys with the aim of grain refining is known as such, as in " Z. Metallkd. 91 (2000) Issue 10, pp. 800-806 described. The effect of known Al-Ti-C master alloys is based on the incorporation of TiC particles, which serve as nucleating agent for the □ mixed crystal, in the melt and requires in the prior art strict compliance with certain parameters in the melt management, such as z. As low as possible melt temperatures and the smallest possible silicon contents to ensure the stability of the TiC particles in the melt and to avoid their reaction with the other alloy components. At silicon contents of more than 3% by weight, according to Greer et al. Advanced Engineering Materials (2003) No. 1-2, pages 81-91 and " Continuous Casting, Ed. by K Ehrke and W. Schneider, DGM (2000 ) A. Tronche and AL Greer, "Effect of Solute Elements on the Grain Structures of Al-Ti-P and Al-Ti-C Grain-Refined Al Alloys", pp. 218-222; 221 , 222) for poisoning of TiC by silicon, so that the grain refining effect of TiC on the □ -aluminium mixed crystal phase in the Al-Si casting alloys is prevented. The effect of carbon on the intermetallic compounds, the primary silicon, and the eutectic phases in Al-Si cast alloys without affecting the □ mixed crystal phase (ie, without grain refining effect by carbon or carbide in this phase) has not been previously known.

Although good mechanical values are already present in the cast state, castings produced from the alloy according to the invention can be subjected to all heat treatments.

The aluminum-silicon casting alloys according to the invention are particularly suitable for casting pistons and other machine parts for internal combustion engines, for cylinder heads, crankcases, liners or engine blocks. The solution of the object of the invention therefore also includes these uses.

With reference to the figures and examples, the invention is to be further illustrated, without the examples being limiting. The person skilled in the art can easily carry out the invention with the aid of what is clearly illustrated in examples and figures throughout the scope given above.

• Fig. 1 zeigt das Mikrogefüge einer AlSi12CuNiMg-Sekundärlegierung, x 500
• Fig. 2 zeigt das Mikrogefüge einer erfindungsgemäß legierten AlSi12CuNiMg-Sekundärlegierung unter Zugabe von Kohlenstoff, x 500
• Fig. 3 zeigt das Mikrogefüge einer AlSi14Cu3Mg-Legierung mit Phosphorzugabe, x 100
• Fig. 4 zeigt das Mikrogefüge einer erfindungsgemäß legierten AlSi14Cu3Mg-Legierung unter Zugabe von Kohlenstoff und Phosphor, x 100

(Maßstab in den Figuren = 50 µm)Show it:

• Fig. 1 shows the microstructure of an AlSi12CuNiMg secondary alloy, x 500
• Fig. 2 shows the microstructure of an alloyed AlSi12CuNiMg alloy according to the invention with the addition of carbon, x 500
• Fig. 3 shows the microstructure of a AlSi14Cu3Mg alloy with phosphorus addition, x 100
• Fig. 4 shows the microstructure of an alloyed AlSi14Cu3Mg alloy according to the invention with the addition of carbon and phosphorus, x 100

(Scale in the figures = 50 μm)

example 1 Near-eutectic Al-Si casting alloy with carbon

The AlSi12CuNiMg secondary alloy was selected as a representative of the large group of Al-Si casting alloys. The experimental alloy was in cylindrical specimens with a casting temperature of 780 ° C in a reduced to 300 ° C. heated steel mold. Carbon was added using the self-made Al-Ti-C master alloy.

A medium-frequency induction furnace was used to produce the AlTi6C1 master alloy. 2000 g of AlTi6 master alloy were first melted at 1400 ° C in a graphite crucible. To this melt was added 30 grams of graphite powder wrapped in aluminum foil. The casting of the Al-Ti-C prealloy thus prepared was carried out after a holding time of about 30 in a copper mold. The master alloy consists of an aluminum matrix, in which Al ₃ Ti and TiC particles are embedded.

Table 1 shows the composition of the alloys investigated. <u> Table 1. </ u> Composition of Al-Si Cast Refining,% by Weight Si C Cu Ni mg Fe Mn Cr Ti Zn Erfg. Leg. 1 12.4 0,003 1.3 0.8 1.4 1.2 0.3 0.15 0.07 0.3 Vergl.Leg. 2 12.6 - 1.5 0.9 1.6 1.3 0.4 0.13 0.05 0.4

The results of the metallographic investigations are summarized in Table 2. <u> Table 2. </ u> The degree of improvement and the length of the intermetallic particles in the alloy AlSi12CuNiMg investigated finishing degree Length of intermetallic particles, μm Erfg. Leg. 1 Grade 6: well finished 20-30 Comp. Leg. 2 Grade 3: partially finished 100-600

The secondary alloy AlSi12CuNiMg has very coarse needle-shaped iron-containing phases (predominantly Al5FeSi needles) in the cast structure, Fig. 1 , In contrast, alloying with the carbon causes both a well-refined eutectic and precipitates of small intermetallic phases in a very uniform distribution, Fig. 2 ,

Example 2 Hypereutectic Al-Si alloy with carbon

In this example, a hypereutectic Al-Si casting alloy was compared to the alloy of the invention having an approximately similar composition, Table 3. Both alloys were treated with an equal amount of phosphorus. <u> Table 3 </ u> Composition of hypereutectic Al-Si casting alloys, wt% Si Cu C mg Fe Mn Ti Zn P Erfg. Leg. 3 14.1 3.7 0.02 0.33 0.94 0.29 0.21 0.33 0,006 Comp. Leg. 4 14.6 4.1 - 0.32 0.73 0.28 0.22 0.35 0,006

A simultaneous refining of the primary silicon and the Al-Si eutectic was not possible until now, Fig. 3 , Our results show that phosphorus and carbon do not interfere with each other in their effect. Figure 4 shows that with a carbon content of 0.005% by weight a good refining of the primary silicon and an acceptable degree of finishing of the eutectic silicon can be achieved. The compact design and homogeneous distribution of the intermetallic phases in the alloy according to the invention is also of great technological advantage.

Example 3 Improvement of the mechanical properties of Al-Si cast alloys

The positive influence of carbon on Al-Si alloys also clearly reflects the mechanical properties already achieved in the cast state, Table 4 and Table 5. <u> Table 4. </ u> Chemical composition of the alloys studied Si C Cu Ni mg Fe Mn Zr Ti Zn Erfg. Leg. 5 11.8 0,025 1.8 0.8 0.7 0.7 0.3 0.1 0.18 0.4 Comp. Leg. 6 12.5 - 1.5 1.1 1.1 0.4 0.3 - 0.15 0.1 Mechanical properties Testing at RT Mechanical properties after pre-storage at 250 ° C / 100 h test at 250 ° C R _m, MPa R _p0.2 , MPa A ₅ ,% R _m, MPa R _p0.2 , MPa A ₅ ,% Erfg. Leg. 5, F 241 171 0.6 147 105 3.2 Comp. Leg. 6, F 225 152 0.7 112 83 9.3 R _m - tensile strength (MPa); R _p0.2 - yield strength (MPa); A ₅ % - elongation at break in%

The alloy 5 according to the invention has a good strength for a casting alloy, as results from the above-mentioned tabular data. In addition, the alloy 5 according to the invention has a significantly better heat resistance than the comparative alloy 6, the R _p0.2 value of which drops sharply at 250 ° C. after a preliminary storage at 250 ° C. when the mechanical properties are measured at 250 ° C.

By "heat-resistant" we mean here an alloy whose R _p0.2 value after storage at 250 ° C. for at least 50 h, tested at 250 ° C., is above 55 MPa.

Claims (13)

An aluminum-silicon casting alloy comprising 5 to 25% by weight of silicon and at least 65% by weight of aluminum as main alloying constituents and optionally further constituents and unavoidable impurities, characterized in that the alloy contains 0.0007 to 0.1% by weight of carbon contains. Aluminum-silicon casting alloy according to claim 1 with 5 to 25 wt .-% silicon and 0.0007 to 0.1 wt .-% carbon and in each case to 4 wt .-% of at least one of the following and in total to 10 wt. % of the following alloy constituents: magnesium, manganese, iron, cobalt, copper, zinc, nickel, vanadium, niobium, molybdenum, chromium, tungsten, beryllium, lead, lithium, yttrium, cerium, scandium, hafnium, silver, zirconium, titanium, boron , Strontium, sodium, potassium, calcium, antimony, sulfur, barium, phosphorus, and balance at least 65% by weight of aluminum including unavoidable impurities. Aluminum-silicon casting alloy according to claim 1 or 2, characterized in that the alloy contains 5 to 18 wt.%, In particular 12.5 to 14.5 wt .-% silicon. Aluminum-silicon casting alloy according to one of claims 1 to 3, characterized in that present in its microstructure fine primary silicon and grafted eutectic simultaneously. Aluminum-silicon casting alloy according to one of claims 2 to 4, characterized in that intermetallic phases are present in their structure as needles or small platelets up to a maximum of 40 microns in length. Aluminum-silicon casting alloy according to one of claims 1 to 5, obtainable by targeted adjustment of the carbon content to 0.0007 to 0.1 wt .-%. A method for producing an aluminum-silicon casting alloy according to any one of claims 1 to 5, characterized in that the carbon content is adjusted by addition of carbon in any desired form. A method according to claim 7, characterized in that the constituents selected for the composition melted together, while heated to a temperature in the interval of 650 ° C to 1,000 ° C, preferably from 720 ° C to 950 ° C and poured into a mold. A method according to claim 7 or 8, characterized in that the carbon content is achieved by adding chemical carbon compounds and / or their mixtures, in particular by adding powdered carbides and carbonitrides, also in the form of a sintered product of carbides and carbonitrides. A method according to claim 7 or 8, characterized in that a carbon-containing aluminum master alloy is introduced into the melt from the other components provided for the alloy or added in advance to the components to be melted. A method according to claim 10, characterized in that an aluminum-titanium-carbon master alloy is used. Method according to one of claims 7 to 11, characterized in that the master alloy in addition to carbon also contains phosphorus. Use of the aluminum casting alloy according to one of claims 1 to 6 for casting thermally highly stressed machine elements, in particular pistons, cylinder heads, crankcases, liners or engine blocks in each case for internal combustion engines.

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