High heat-resistant aluminium casting alloy and casting for combustion engines cast from such an alloy

Abstract

The present invention relates to an aluminium casting alloy having (in % by weight) Cu: 6.0-8.0%, Mn: 0.3-0.055%, Zr: 0.18-0.25%, Si: 3.0-7.0%, Ti: 0.05-0.2%. Sr: up to 0.03%, V: up to 0.04%, Fe: up to 0.25%, remainder aluminium and unavoidable impurities, and a casting for a combustion engine. The aluminium casting alloy according to the invention has high mechanical properties after a longer operating duration at high temperatures and at the same time can be cast without any problems. Furthermore, the casting according to the invention has optimised mechanical properties during operation at high temperatures and at the same time can be produced in an operationally reliable manner in terms of casting technology.

Claims

1. An aluminium casting alloy, consisting of (in % by weight) TABLE-US-00008 Cu: 6.0-8.0% Mn: 0.3-0.55% Zr: 0.18-0.25% Si: 3.0-7.0% Ti: 0.05-0.2% Sr: up to 0.03% V: up to 0.04% Fe: up to 0.25% remainder aluminium and unavoidable impurities.

2. The aluminium casting alloy according to claim 1, wherein, the Si content is less than 5.0% by weight.

3. The aluminium casting alloy according to claim 2, wherein, the Si content is at least 3.5% by weight.

4. The aluminium casting alloy according to claim 1, wherein, the Si content is at least 5.0% by weight.

5. The aluminium casting alloy according to claim 4, wherein, the Si content is at least 5.5% by weight.

6. The aluminium casting alloy according to claim 1, wherein, the Cu content is at most 7.0% by weight.

7. The aluminium casting alloy according to claim 1, wherein, the Mn content is 0.4-0.55% by weight.

8. The aluminium casting alloy according to claim 1, wherein, the Zr content is 0.2-0.25% by weight.

9. The aluminium casting alloy according to claim 1, wherein, the Ti content is 0.08-0.12% by weight.

10. The aluminium casting alloy according to claim 1, wherein, the Sr content is at least 0.015% by weight.

11. A casting for a combustion engine, cast from an aluminium casting alloy formed according to claim 1.

12. The casting according to claim 11, wherein, the casting is a cylinder head.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, the invention is explained in more detail by means of exemplary embodiments. Herein are shown:

(2) FIG. 1 a diagram in which the respective mechanical properties, determined at room temperature, of casting samples made from three aluminium casting alloys according to the invention E1, E2, E3 are compared to the mechanical properties of a casting sample made from a comparison alloy V, each in the T6W state;

(3) FIG. 2 a diagram in which the respective tensile strength Rm, yield strength Rp0,2 and ultimate strain A, determined at 300 C., of casting samples of the three aluminium casting alloys according to the invention E1, E2, E3 and the comparison sample V are compared after a respective heat treatment implemented at 300 C. over 500 hours.

(4) FIG. 3 a diagram in which the respective tensile strength Rm and yield strength Rp0,2, determined at 250 C., of casting samples of the aluminium casting alloy according to the invention E1 and the standard casting alloys AlSi6Cu4 and AlSi7Cu0.5Mg are compared after a respective heat treatment implemented at 250 C. over 500 hours.

(5) FIG. 4 a diagram in which the respective tensile strength Rm and yield strength Rp0,2, determined at 300 C., of casting samples of the aluminium casting alloy according to the invention E1 and the standard casting alloys AlSi6Cu4 and AlSi7Cu0.5Mg are compared after a respective heat treatment implemented at 300 C. over 500 hours.

DESCRIPTION OF THE INVENTION

(6) Three aluminium casting alloys according to the invention E1, E2, E3 were melted, the composition of which is specified in Table 1. For comparison, a comparison alloy V was melted, the composition of which that is likewise listed in Table 1 corresponds to the known aluminium casting alloy AlCu7MnZr.

(7) Cylinder heads were cast from the aluminium casting alloys E1, E2, E3, V, which underwent a T6W treatment after solidification. Therein, the cylinder heads are solution annealed at 480-500 C. respectively over seven and a half hours, are subsequently quenched with water and then aged over four hours at 240 C. Subsequently, the mechanical properties, tensile strength Rm, yield strength Rp0,2, Brinell hardness HB and ultimate strain A are determined for the thus treated cylinder heads in the region of the combustion chambers. Therein, respectively forty casting samples consisting of the aluminium casting alloy E1 and E2 and respectively fifteen casting samples consisting of the aluminium casting alloy E3 and the comparison alloy V were tested. The arithmetic average of the mechanical properties determined for each of the casting samples are specified in Table 2 in detail and are summarised in FIG. 1 graphically.

(8) In order to test the temperature influence on the long-term development of the mechanical characteristic values, cylinder heads cast from the aluminium casting alloys E1, E2 and V underwent a long-term heat treatment in which they were kept at a temperature of 300 C. firstly over a duration of eight hours, then over a duration of 100 hours and finally over a duration of 300 hours. A sample was taken from the combustion chamber for each of the thus heat-treated cylinder heads after completion of each heat treatment duration and the yield strength Rp0,2, the tensile strength Rm and the ultimate strain A were determined at room temperature for these casting samples. The arithmetical average of the mechanical properties determined for the thus treated casting samples are specified in Table 3. The test results show that after 100 hours, the tensile strength Rm and the yield strength Rp0,2 are substantially stable in the case of the cylinder heads cast from the aluminium casting alloys according to the invention E1, E2, whilst the ultimate strain A increases. The cylinder heads produced from the comparison alloy each have, on the other hand higher strengths, however their ultimate strain A lies clearly below the ultimate strain A determined for the samples according to the invention respectively.

(9) Finally, further cylinder heads produced from alloys according to the invention E1, E2, E3 and V underwent a long-term heat treatment which was likewise carried out at 300 C. and which extended over 500 hours. Then also here the yield strength Rp0,2, the tensile strength Rm and the ultimate strain A were determined for 300 C. samples which were in turn taken from the region of the combustion chamber. The arithmetical average values formed therein from the obtained values are listed in Table 4 and summarised in FIG. 2.

(10) Additionally to the tests on the samples produced from the alloys according to the invention E1, E2, E3 and from the high heat-resistant alloy V, comparisons were also made to conventional standard casting alloys, the castability of whichin contrast to the comparison alloy V which has a clearly poorer castabilityis comparable to the castability of the alloys according to the invention. For this purpose, the same cylinder heads as for the samples of E1, E2, E3 and V were produced from the standard casting alloys S1 and S2, the compositions of which that are listed in Table 5 correspond to the known aluminium casting alloys AlSi7Cu0.5Mg and AlSi6Cu4. The cylinder heads cast from the standard alloys S1 and S2 each underwent the heat treatments which are typical for them. Thus the cylinder heads cast from the alloy S1 underwent a T6 air heat treatment and the cylinder heads cast from the alloy S2 underwent a T6W heat treatment.

(11) In order to compare the heat resistance of the alloys according to the invention to the standard alloys used today, samples produced from the alloys S1, S2 and the alloy according to the invention E1 underwent a long-term heat treatment implemented at 250 C. and extending over 500 hours. Then also here the yield strength Rp0,2 and the tensile strength Rm were determined for 250 C. hot samples which were taken from the region of the combustion chamber. The arithmetical average values formed therein from the obtained values are listed in Table 6 and summarised in FIG. 3.

(12) Finally, further cylinder heads generated from the alloy according to the invention E1 and the standard alloys S1 and S2 underwent a long-term heat treatment which was implemented at 300 C. and which extended over 500 hours. Then in turn, the yield strength Rp0,2 and the tensile strength Rm were determined for 300 C. hot samples which were in turn taken from the region of the combustion chamber. The arithmetical average values formed from the thus obtained values are listed in Table 7 and summarised in FIG. 4.

(13) The tests prove that for the cylinder heads cast from the alloys according to the invention E1, E2, E3, no cracks were able to be detected and the structure of the castings was predominantly pore-free. The strength values determined for the castings consisting of the aluminium casting alloys according to the invention E1, E2, E3 are indeed each lower after high temperature loading than in the case of comparison alloy V. For this, the aluminium casting alloys according to the invention E1, E2, E3 can, however, also be cast in large-scale conditions without problem and in an operationally reliable manner. At the same time, the tests prove that the strengths of the cylinder heads cast from aluminium casting alloys according to the invention E1, E2, E3 are double as high as the strengths of standard alloys with comparable castability.

(14) TABLE-US-00001 TABLE 1 Cu Si Zr Ti Mn Fe Zn Sr E1 6.74 3.92 0.21 0.11 0.51 0.12 0.02 E2 6.67 6.28 0.22 0.11 0.51 0.12 0.02 E3 6.58 6.16 0.22 0.12 0.51 0.13 0.02 0.02 V 6.72 0.06 0.22 0.11 0.5 0.08 0.02 Specifications in % by weight Remainder Al and unavoidable impurities

(15) TABLE-US-00002 TABLE 2 Rp0,2 Rm A HB [MPa] [MPa] [%] [] E1 179.4 284.2 2.45 92.5 E2 170.3 266.1 1.75 94.0 E3 173.1 276.7 2.09 96.0 V 178.6 264.5 1.92 93.0

(16) TABLE-US-00003 TABLE 3 Duration [h] Alloy 8 100 500 Rp0,2 E1 123.27 95.72 91.71 [MPa] E2 126.89 101.49 96.46 V 193.67 186.33 193.00 Rm E1 235.69 196.33 190.57 E2 243.78 206.04 194.95 V 263.33 280.67 298.67 A E1 3.46 3.80 4.58 E2 3.51 4.59 4.76 V 1.30 1.87 2.20

(17) TABLE-US-00004 TABLE 4 Rp0,2 Rm A [MPa] [MPa] [%] E1 67.00 88.33 27.73 E2 64.33 86.67 24.47 E3 60.33 82.67 28.47 V 106.33 148.33 21.13

(18) TABLE-US-00005 TABLE 5 Cu Si Sr Ti Mn Fe Zn Mg S1 0.52 7.11 0.02 0.10 0.12 0.14 0.02 0.39 S2 3.97 6.18 0.02 0.11 0.31 0.47 0.34 0.37 Specifications in % by weight, Remainder Al and unavoidable impurities

(19) TABLE-US-00006 TABLE 6 Rp0,2 Rm [MPa] [MPa] S1 79 91 S2 75 90 E1 95 135

(20) TABLE-US-00007 TABLE 7 Rp0,2 Rm [MPa] [MPa] S1 35 42 S2 48 55 E1 65 90