Cast aluminum alloy for structural components

Abstract

Aluminium alloy, in percentages by weight consisting of 11% to 13.5% silicon, 0.2% to 0.5% copper, more than 0.35% to 0.55% magnesium, up to 0.4% iron, up to 0.4% manganese, up to 0.1% titanium, up to 0.5% zinc, more than 0.02% to 0.08% strontium, more than 0.032% to 0.05% boron and the remainder aluminium, wherein iron is present by weight of 0.2% to 0.4% and the ratio of manganese to iron is 0.6 to 1.0.

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to aluminium alloys that can be cast into structural components; non-limiting examples of these include engine blocks, cylinder heads, suspension parts such as shock absorber bridges and wishbones, wheels and aircraft doors.

[0002] Al-Si-based cast aluminum alloys, such as the 300 series aluminum alloys, are widely used for structural components in the automotive, aerospace, and general engineering industries due to their good castability, corrosion resistance, machinability, and especially their high strength-to-weight ratio in the heat-treated condition. Regarding castability, low silicon concentrations are thought to inherently result in poor castability due to the increased solidification range and reduced latent heat. However, at high silicon content (>14%), the coarse primary silicon particles significantly reduce the machinability, formability, and fracture toughness of the materials.

[0003] In Al-Si casting alloys (e.g. alloys 319, 356, 390, 360, 380), strengthening is achieved by heat treatment after casting with the addition of various alloying elements, including but not limited to Cu and Mg.The heat treatment of cast aluminum includes at least one mechanism known as cold aging or precipitation hardening, which, without being limited to this, involves three steps: (1) solution treatment at a relatively high temperature below the alloy's melting point (also defined as T4), often for periods exceeding 8 hours, to dissolve its alloying elements (solution elements) and to homogenize or modify the microstructure; (2) rapid cooling or quenching in cold or warm liquid media, such as water, to retain the dissolved elements in a supersaturated solid solution (SSS); and (3) aging (T5), by holding the alloy at an intermediate temperature for a period of time suitable for achieving hardening or strengthening by precipitation.Solution treatment (T4) serves three main purposes: (1) dissolving elements that will later cause cold aging, (2) rounding off undissolved components, and (3) homogenizing the dissolved concentrations in the material. Quenching after T4 solution treatment serves to keep the dissolved elements in a supersaturated solid solution and also to create supersaturation of defects, which improves diffusion and dispersion of precipitates. To maximize the strength of the alloy, the precipitation of all hardening phases should be prevented during quenching. Aging (T5, either cold or hot aging) produces a controlled dispersion of hardening precipitates.

[0004] The most common Al-Si-based alloy used in the manufacture of motor vehicle engine blocks and cylinder heads is the heat-treatable cast aluminum alloy 319 (nominal composition by weight: 6.5% Si, 0.5% Fe, 0.3% Mn, 3.5% Cu, 0.4% Mg, 1.0% Zn, 0.15% Ti and balance Al) and A356 (nominal composition by weight: 7.0% Si, 0.1% Fe, 0.01% Mn, 0.05% Cu, 0.3% Mg, 0.05% Zn, 0.15% Ti and balance Al). Due to the relatively low silicon content (6–7 wt%) in both alloys, the liquidus temperatures are high (~615 °C for A356 and ~608 °C for 319), resulting in high melting energy utilization and high hydrogen solubility. The large solidification range of both A356 (greater than or equal to 60 °C) and 319 (greater than or equal to 90 °C) also increases the size of the solidification zone and the tendency to shrink.Importantly, both alloys exhibit double microstructures with primary dendritic aluminum grains and eutectic grains (Al + Si). During work hardening, the eutectic grains solidify between the pre-worked dendritic Al networks, making feeding during eutectic shrinkage difficult. In Al alloys with 7% Si, the volume fraction of eutectic grains is approximately 50%. Additionally, engine blocks, and especially cylinder heads, manufactured from such aluminum alloys can undergo thermomechanical fatigue (TMF) over their service life, particularly in high-performance engine applications.

[0005] The addition of strengthening elements, such as copper, magnesium, and manganese, can significantly affect the physical properties of materials, including specific undesirable effects. For example, aluminum alloys with a high copper content (3–4%) have been reported to exhibit unacceptable rates of corrosion, particularly in saline environments. Typical high-pressure die-cast aluminum alloys (HPDC aluminum alloys), such as A 380 or 383, used for transmission and engine components, contain 2–4% copper. It is understandable that the corrosion problem with these alloys becomes more significant when longer warranty periods and higher vehicle mileage are required.

[0006] Although there is a commercial alloy 360 (nominal composition by weight: 9.5% Si, 1.3% Fe, 0.3% Mn, 0.5% Cu, 0.5% Mg, 0.5% Ni, 0.5% Zn, 0.15% Sn and balance Al) intended for corrosion-resistant applications, such an alloy may experience problems with thermal fatigue over its lifetime, especially in high-performance engine applications.

[0007] CN 1 847 429 A describes an aluminum alloy which consists, in percentages by weight, of 11% to 13.5% silicon, up to 0.2% copper, 0.15% to 0.55% magnesium, up to 0.2% iron, up to 0.1% manganese, up to 0.1% titanium, up to 0.1% zinc, 0.015% to 0.08% strontium, 0.01% to 0.05% boron and the remainder aluminum.

[0008] EP 2 455 505 A1 describes a similar aluminium alloy, but containing 6% to 12% silicon, 0.0015% to 3% copper, 0.05% to 1% magnesium, up to 0.5% iron, up to 0.4% manganese, up to 0.12% titanium, up to 0.4% zinc and either up to 0.03% strontium and less than 0.01% boron or less than 0.01% sr and up to 0.025% boron.

[0009] In DE 10 2009 019 269 A1 a similar aluminium alloy is also described, which, however, contains 11.5% to 12.1% silicon, up to 0.2% copper, 0.003% to 0.4% magnesium, up to 0.35% iron, 0.4% to 0.71% manganese, up to 0.25% titanium and up to 0.03% strontium.

[0010] DE 10 2010 055 011 A1 describes a similar aluminium alloy, which, however, can contain a higher copper content of up to 0.6%.

[0011] A similar aluminum alloy is described in DE 10 2008 046 803 A1.

[0012] DE 10 2007 012 424 A1 also describes a similar aluminium alloy, which, however, contains a maximum of 0.25% copper, up to 0.1% zinc and up to 0.02% strontium.

[0013] Similar aluminium alloys are also described in DE 20 2006 006 518 U1.

[0014] Furthermore, US 2005 / 0 109 429 A1 also describes similar aluminum alloys.

[0015] Furthermore, in Drossel, G. et al.: Aluminium-Taschenbuch, Volume 2, 15th edition, Düsseldorf: Aluminium-Verlag, 1996, on pages 396 to 402, it is described that boron can be used as an agent for grain refinement in aluminium alloys, while strontium can be used as an agent for the refinement of Al-Si alloys.

[0016] One object of the invention is to provide improved castable aluminium alloys and a method for casting a motor vehicle component from such alloys, which are suitable for both sand and metal casting and with which castings with reduced casting porosity and improved alloy strength as well as improved fatigue and corrosion resistance can be produced, particularly for applications at elevated temperatures. SUMMARY OF THE INVENTION

[0017] This problem is solved with an aluminium alloy having the features of claim 1 and a method having the features of claim 6.

[0018] The aluminum alloy consists, in percentage proportions by weight, of 11% to 13.5% silicon, 0.2% to 0.5% copper, more than 0.35% to 0.55% magnesium, up to 0.4% iron, up to 0.4% manganese, up to 0.1% titanium, up to 0.5% zinc, more than 0.02% to 0.08% strontium, more than 0.032% to 0.05% boron, and the remainder aluminum.

[0019] The method for casting a motor vehicle component from an aluminum alloy, such that thermal fatigue is reduced, comprises: providing a mold; and introducing a molten aluminum alloy into the mold, wherein the aluminum alloy, in percentages by weight, consists substantially of 11% to 13.5% silicon, 0.2% to 0.5% copper, more than 0.35% to 0.55% magnesium, up to 0.4% iron, up to 0.4% manganese, up to 0.1% titanium, up to 0.5% zinc, more than 0.02% to 0.08% strontium, more than 0.032% to 0.05% boron, and the remainder being aluminum, and wherein the thermal fatigue of the motor vehicle casting is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following detailed description of special embodiments can best be understood when read in conjunction with the following drawings, where identical structures are indicated by the same reference numerals and where: Fig. Figure 1 represents a cast cylinder head, demonstrating the complexity of the casting geometry. Fig. Figure 2 shows a graph of the effect of the addition of boron on the eutectic grains in Al with 12.3% Si, 0.41% Mg, 0.25% Cu, 0.15% Fe, 0.026% Sr by a quantitative metallographic analysis. DETAILED DESCRIPTION

[0021] Embodiments described herein create improved castable aluminium alloys suitable for both sand and metal forming casting, from which castings with reduced casting porosity and improved alloy strength, as well as improved fatigue and corrosion resistance, can be produced, especially for applications at elevated temperatures.

[0022] First on Fig. Referring to Figure 1, a cylinder head 1 is shown. Aspects of the cylinder head 1 include (in addition to the cylinders) a chain guard 2, a cover surface 3 (which contacts the gasket and is mounted to the engine block), and an exhaust port 4. In Fig. Figure 1 also shows the combustion dome 5, a water jacket passage 6 and an inlet passage 7. Various embodiments of cylinder heads are considered here, such as automotive cylinder heads.

[0023] Photomicrographs (not shown) were examined and indicate that the microstructure of specific embodiments described herein exhibits an alloy containing fine eutectic dendritic grains, whereas prior art microstructure analysis shows the presence of large eutectic silicon particles and coarse aluminum dendrites. The microstructure of the specific embodiments described herein shows fine eutectic silicon fibers and also eutectic aluminum dendrites. In cast aluminum alloys, the fineness of the microstructure is influenced by the cooling rate as the casting solidifies from the liquid. For the same cooling conditions, the specific embodiments of the proposed alloy produce much finer eutectic silicon particles compared to the prior art through the addition of strontium and, in particular, boron for eutectic grain refinement.Finer grains offer the advantages of improved mechanical properties, such as higher tensile strength, increased deformability and increased fatigue resistance.

[0024] The eutectic silicon fibers of special embodiments described herein are very fine and less than one micrometer in size. In contrast, a prior art microstructure analysis shows that these contain large eutectic silicon particles (larger than ten micrometers). An analysis of the microstructure of the cast aluminum alloy containing 12.6% Si, 0.3% Mg, 0.25% Cu, 0.18% Fe, 0.045% Sr, and 0.026% B demonstrates the fineness of the eutectic silicon fibers. The size of the eutectic Si fibers is less than 1 µm (micrometer).

[0025] Typically, the microstructural constituents are quantified using quantitative metallurgy. Quantitative metallurgy is usually performed in an image analyzer using metallurgically polished samples. All samples for quantitative metallographic analysis were prepared using standard techniques. After surface preparation with 1 µm diamond, final polishing was achieved using a commercial SiO₂ abrasive suspension (Struers OP-U). For specific testing purposes, the polished samples underwent further preparation. Silicon particles were typically quantified on fully heat-treated samples based on their mean aspect ratio, their area-equivalent circle diameter, their form factor (roundness, SF = P² / 4πA, where P is the particle circumference and A is the particle area), their length, and their area fraction of the polished section.Approximately 100 fields with 5,000–10,000 particles each were measured for every sample. Since automated measurement of particle characteristics depends to some extent on the grayscale setting of the instrument, the detection level was set to approximately 60% of the aluminum grayscale.

[0026] An analysis of macrographs (not shown) of eutectic grains as they appear was performed, which differ by variations in magnesium levels for the specific embodiments described herein. The analysis included alloys containing (in addition to varying amounts of magnesium) 13% silicon and 0.02% strontium. Specifically analyzed were different additions of magnesium under steady-state hardening with a temperature gradient of approximately 2.1°C / mm and a growth rate of 0.1 mm / s. For the alloy with one addition of magnesium, the eutectic growth morphology appears cellular, with a cell spacing of approximately 1.7 mm.Unlike other single-phase alloys, the cellular eutectic grain boundary is not so straight, and instead exhibits small branches, which are thought to be related to the interaction with gas bubbles that form in the samples. When 0.35% Mg is added to the alloy, columnar eutectic grains with apparent cross-branching are formed, although these are not well-developed. The primary dendrite spacing of the eutectic grains is approximately 1.8 mm. When the magnesium addition increases to 0.45%, the eutectic grains become equiaxial dendrites with a mean grain size of 0.8 mm. Importantly, the level of microporosity is significantly reduced except at the sample periphery. When the alloy contains 0.6% magnesium, a directional columnar grain structure can be observed.The solid sample exhibits an even lower level of porosity (microporosity) than other alloys shown. Likewise, the eutectic structure consists of a large number of small, spherical grains of varying sizes, with an average size of 0.1 mm. These small, equiaxial eutectic grains do not exhibit any branching; this indicates that a large number of heterogeneous sites were active in eutectic nucleation. From this, it can be concluded that during the solidification of this alloy (0.6% Mg), primary aluminum dendrites initially grow to the point of protruding into the liquid, and that subsequently, a large number of eutectic grains continuously form nuclei to create the fine, equiaxial eutectic grains. In the specific embodiments where a magnesium level of 0.6% was analyzed, the alloy also contained 0.04% boron.

[0027] A comparison of the architecture of specific embodiments of the proposed alloy with a widely used cast alloy from the prior art also shows that the proposed alloy is less porous (even when the same casting conditions were used). Such less porous alloys offer specific advantages, including increased strength.

[0028] With reference to Fig. 2 shows Fig. 2 A graph of the effect of the addition of boron on the size of the eutectic grains in an Al alloy with 12.3% Si, 0.41% Mg, 0.25% Cu, 0.15% Fe, 0.026% Sr by a quantitative metallographic analysis.

[0029] In the specific embodiments described herein, the copper content is maintained in a range of up to approximately 0.5%. This is advantageous because the presence of a high copper content (such as 3–4%) can significantly influence the solidus and thus the solidification range (liquidus-solidus) of the alloy. For two similar alloys, one with 3–4% copper and the other with 0.5% copper, the solidus for the first alloy can be 500°C and for the second alloy 545°C; the solidification range for the first alloy can be 70°C and for the second 25°C. The second alloy offers advantages, such as a reduced tendency to develop shrinkage porosity.

[0030] According to another aspect of the various embodiments, an aluminum alloy is described herein which, in percentage proportions by weight, essentially consists of approximately 11% to approximately 13.5% silicon, up to approximately 0.5% copper, approximately 0.15% to approximately 0.55% magnesium, up to approximately 0.4% iron, up to approximately 0.4% manganese, up to approximately 0.1% titanium, up to approximately 0.5% zinc, approximately 0.015% to approximately 0.08% strontium, approximately 0.01% to approximately 0.05% boron, and the remainder being aluminum.

[0031] According to specific embodiments, an aluminum alloy is described herein which, in percentage proportions by weight, essentially consists of 11% to 13.5% silicon, 0.2% to 0.5% copper, more than 0.35% to 0.55% magnesium, up to 0.4% iron, up to 0.4% manganese, up to 0.1% titanium, up to 0.5% zinc, more than 0.02% to 0.08% strontium, more than 0.032% to approximately 0.05% boron, and the remainder being aluminum. EXAMPLES

[0032] The described embodiments are made more understandable by reference to the following examples, which are offered for illustration and which a person skilled in the art will recognize are not intended to be restrictive. EXAMPLE 1

[0033] A melt of an alloy of embodiments comprising, nominally by weight, 11.8% Si, 0.33% Mg, 0.2% Fe, 0.034% Sr, and 0.032% B, with the remainder being aluminum and random impurities (embodiment 1), was prepared by the following steps. The correct amounts of master alloys containing Al and 10% Si, Al and 50% Si, Al and 25% Fe, and Al and 25% Mn (by weight) and of pure magnesium metal were carefully weighed and melted in a clay-graphite crucible in an electric resistance furnace. Once degassed and purified, the melt was treated with an active ingredient to induce a eutectic aluminum-silicon phase and / or an intermetallic phase modification.

[0034] A preferred active ingredient for this purpose comprises Sr and B. The preferred method is to use master alloys containing Al and 10% Sr and Al and 3% B (by weight), which are added to the melt during the final stages of outgassing, provided that no halogenated material is used. After this processing, the alloy composition and gas content were verified, and the alloy melt was gravity-cast into metal molds to form at least five test blocks with dimensions of 12.7 mm in cross-sectional diameter and approximately 200 mm in length.

[0035] The cast test blocks were subsequently subjected to T6 heat treatment (solution-treated at 535±5 °C for 8 hours, then quenched with hot water (50 °C) and subsequently stored at 155±5 °C for 3 hours). A tensile test was performed using ASTM procedures B557.

[0036] For comparison, a melt of conventional aluminum alloy A356 was prepared and cast in a similar manner to provide test ingots, which were further heat-treated in the T6 condition (solution-treated at 535±5 °C for 8 hours, then quenched with hot water (50 °C) and subsequently aged at 155±5 °C for 3 hours). The tensile testing of the specimens was carried out in a similar manner.

[0037] Table 1 presents the results of the mechanical properties testing, where UTS is the tensile strength (in MPa) and percent elongation is the plastic strain at fracture. TABLE 1 alloy UTS % Elongation mean minimum mean minimum Design 1 as cast 270,5 262,4 9,8 7,6 Design 1T6 345,2 334,7 15,1 13,0 A356 T6 262 254 1,5 1,2

[0038] Referring to the alloy formulation in Example 1, it is evident that the alloy test specimens exhibited a better combination of tensile strength and elongation compared to the test specimens of the conventional alloy A356. Furthermore, it is important to note that the alloy test specimens showed a significantly higher elongation compared to the A356 test specimens. Consequently, the alloys described herein can enable the design of lighter castings, as the castings exhibit improved mechanical properties and can be designed with reduced cross-sectional thickness. EXAMPLE 2

[0039] A melt of an alloy of embodiments comprising nominally, by weight, 12.6% Si, 0.3% Mg, 0.18% Fe, 0.045% Sr, and 0.026% B, with the remainder being Al and incidental impurities (embodiment 2), was prepared by the steps described above for Example 1. The melting, casting, heat treatment, and tensile testing of the test specimens are the same as those described above for Example 1.

[0040] Table 2 presents the results of the mechanical properties testing, where UTS is the tensile strength (in MPa) and percent elongation is the plastic elongation at fracture. TABLE 2 alloy UTS % Elongation mean minimum mean minimum Design 2 as cast 260,4 251,4 8,5 7,1 2T6 design 330,8 321,9 14,2 12,8 A356 T6 262 254 1.5 1,2

[0041] Regarding the alloys of the described embodiments, it is again evident that the alloy test specimens exhibited a better combination of tensile strength and elongation compared to the test specimens of the conventional alloy A356. Furthermore, it is important to note that the alloy test specimens showed a very high elongation compared to the alloy A356 test specimens. EXAMPLE 3

[0042] A melt of an alloy of embodiments comprising nominally, by weight, 13.25% Si, 0.25% Mg, 0.19% Fe, 0.048% Sr, and 0.022% B, with the remainder consisting of Al and accidental impurities (embodiment 3), was prepared by the steps described above for Example 1. The melting, casting, heat treatment, and tensile testing of the test specimens are the same as those described above for Example 1.

[0043] Table 3 presents the results of the mechanical properties testing, where UTS is the tensile strength (in MPa) and percent elongation is the plastic elongation at fracture. TABLE 3 alloy UTS % Elongation mean minimum mean minimum embodiment 3 as cast 254,7 247,2 8,0 6,9 Design 3T6 325,3 317,7 13,5 11,7 A356 T6 262 254 1,5 1,2

[0044] With regard to the specific embodiments of the alloys described herein, it is again evident that the test specimens of the special alloys exhibited a better combination of tensile strength and elongation compared to the test specimens of the conventional alloy A356. Furthermore, it is important to note that the test specimens of the alloys described herein showed a very high elongation compared to the test specimens of alloy A356. EXAMPLE 4

[0045] A melt of an alloy of embodiments comprising nominally, by weight, 12.3% Si, 0.41% Mg, 0.25% Cu, 0.15% Fe, 0.026% Sr, and 0.032% B, with the remainder consisting of Al and accidental impurities (embodiment 4), was prepared by the steps described above for Example 1. The melting, casting, heat treatment, and tensile testing of the test specimens are the same as those described above for Example 1.

[0046] The described embodiments offer significant advantages compared to conventional alloys, for example, with regard to tensile strength, yield strength, and fatigue and elongation properties. The properties of an alloy of the specific embodiments described herein are compared with one of the most common Al-Si-based alloys used in the manufacture of engine blocks and cylinder heads (A356, 7.0% Si, 0.58% Mg, 0.15% Cu, 0.13% Fe, 0.013% Sr, and 0.013% Ti, with the balance being Al). As can be seen from Tables 4 and 5, the embodiments described herein offer significant advantages, such as with regard to elongation properties at room temperature and at high temperatures. For the sake of completeness, versions such as cast and T6 versions are included in the comparison. TABLE 4 Tensile properties at room temperature alloy UTS, MPa YS, MPa % Elongation mean minimum mean minimum mean minimum A356 Weighing pots 179,8 168,8 115,6 109,2 4,4 3,6 T6 266,9 252,4 210,4 204,6 6,7 4,9 Design 4 Weighing pots 198,4 189,3 108,1 102,5 6,5 5,4 T6 297,6 288,8 230,5 222,4 11,5 9,8 TABLE 5 Tensile properties at high temperature alloy 100°C 150°C 200°C mean minimum mean minimum mean minimum A356T6 UTS,MPa 151,8 142,7 144,7 139,2 142,1 137,5 %Elongation 3,9 3,3 3,3 3,1 2,4 2,2 Design 4 UTS,MPa 200,7 196,1 174,6 169,7 151,5 147,33 %Elongation 9,5 8,7 9,3 8,5 8,4 7,9 EXAMPLE 5

[0047] A melt of an alloy of embodiments comprising nominally, by weight, 12.2% Si, 0.51% Mg, 0.20% Cu, 0.18% Fe, 0.025% Sr, 0.03% Ti, and 0.041% B, with the remainder consisting of Al and accidental impurities (embodiment 5), was prepared by the steps described above for Example 1. The melting, casting, heat treatment, and tensile testing of the test specimens are the same as those described above for Example 1.

[0048] The described embodiments offer significant advantages compared to conventional alloys, for example, with regard to tensile strength, yield strength, and fatigue and elongation properties. The properties of an alloy of the specific embodiments described herein are compared with one of the most common Al-Si-based alloys used in the manufacture of engine blocks and cylinder heads (A356, 7.0% Si, 0.58% Mg, 0.15% Cu, 0.13% Fe, 0.013% Sr, and 0.013% Ti, with the balance being Al). As can be seen from Table 6, the embodiments described herein offer significant advantages, such as with regard to elongation properties at room temperature and at high temperatures. For the sake of completeness, versions such as cast and T6 versions are included in the comparison. TABLE 6 Tensile properties at room temperature alloy UTS, MPa YS, MPa % Elongation mean minimum mean minimum mean minimum A356 Weighing pots 179,8 168,8 115,6 109,2 4,4 3,6 T6 266,9 252,4 210,4 204,6 6,7 4,9 Design 5 Weighing pots 192,3 187,2 106,5 103,2 5,6 5,1 T6 314,7 306,4 269,1 260,2 6,3 5,4 EXAMPLE 6

[0049] For the specific embodiments of the alloy(s), a titanium-containing grain refiner is not required because the alloy(s) do not contain, or contain, primary aluminum grains that require refinement. A titanium-containing grain refiner serves to refine primary aluminum dendrite grains. The primary aluminum grains appear as branching formations that first form in the liquid metal when it is cooled below the liquidus (~615 °C for an A356 alloy containing 6–7% Si). The primary aluminum dendrite grains can only be observed in a hypoeutectic alloy (the initial alloy composition contains less than 11.8% Si). The eutectic grains form at a eutectic temperature of approximately 570 °C or below.The eutectic reaction (liquid → Al + Si) occurs after the primary aluminum dendrite grains in the hypoeutectic alloy (the eutectic reaction being the phase transformation from liquid with an alloy composition of Al and 11.8% Si) in an Al-Si-based alloy system simultaneously transform into solid phases of Al and Si. In the eutectic reaction, the eutectic aluminum phase lacks a dendritic morphology. The eutectic aluminum phase, together with the scale-like or fibrous silicon phase, forms spherical eutectic grains. The eutectic reaction (liquid → Al + Si) also occurs when the remaining liquid composition becomes eutectic (Al and 11.8% Si). Instead, compound B is required to refine the eutectic grains in specific embodiments. The present alloy is a eutectic alloy with fewer primary aluminum dendrite grains.In the special embodiments, a refinement of the eutectic grains was achieved in the present experiments with a combination of Mg (>0.35%), Sr (>0.02%) and B (>0.04%).

[0050] In the melt treatment, the base alloy without sr and boron was first melted in a furnace at a temperature of 760 °C. After holding for 30 minutes, a master alloy containing aluminum and 10 wt% sr was added to the melt at approximately 720 °C, with controlled sr content. After the sr was added, the melt was held for at least another 30 minutes before boron was added for grain refinement. Before pouring the molten melt into a mold, the master alloy containing aluminum and 4% boron was added to the melt at approximately 700 °C, with controlled boron content at approximately 0.04%.

[0051] It is understood that the invention is not limited to the specific embodiments or constructions described above, but that various modifications can be made to it without deviating from the spirit and scope of the invention as set out in the attached claims.

Claims

[1] Aluminium alloy, in percent by weight consisting of 11% to 13.5% silicon, 0.2% to 0.5% copper, more than 0.35% to 0.55% magnesium, up to 0.4% iron, up to 0.4% manganese, up to 0.1% titanium, up to 0.5% zinc, more than 0.02% to 0.08% strontium, more than 0.032% to 0.05% boron and the remainder aluminium, wherein iron is present by weight of 0.2% to 0.4% and the ratio of manganese to iron is 0.6 to 1.

0. [2] Cast cylinder head for an internal combustion engine formed from the alloy according to claim 1. [3] Engine block, wheel, suspension part and / or aircraft door formed from the alloy according to claim 1. [4] Aluminium alloy according to claim 1, wherein the total impurity is less than 0.15%. [5] Aluminium alloy according to claim 1, wherein the percentage of silicon ranges from 13% to 13.5%. [6] Method for casting a motor vehicle component from an aluminium alloy, such that thermal fatigue is reduced, comprising: a mold is provided; and an aluminum alloy melt is introduced into the mold, wherein the aluminum alloy consists in percentage proportions by weight of 11% to 13.5% silicon, 0.2% to 0.5% copper, more than 0.35% to 0.55% magnesium, up to 0.4% iron, up to 0.4% manganese, up to 0.1% titanium, up to 0.5% zinc, more than 0.02% to 0.08% strontium, more than 0.032% to 0.05% boron and the remainder aluminum, and wherein the thermal fatigue of the automotive casting is reduced, where iron is present in a concentration of 0.2% to 0.4% by weight and the ratio of manganese to iron is 0.6 to 1.0.

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