AL-CASTING ALLOY

Abstract

The invention relates to an Al casting alloy.

Description

The invention relates to an aluminum casting alloy.

DE 10 2008 055 928 A1, DE 10 2012 108 590 A, DE 10 2013 108 127 A1 and DE 10 2014 101 317 A1 disclose various low-Si Al casting alloys.

Proceeding from this prior art, it is an object of the present invention to provide an improved low-Si Al casting alloy which has especially been further developed with regard to its mechanical properties.

This is achieved in accordance with the invention by an Al casting alloy containing at least five of the following alloy constituents:

Si: 3.0% to 3.8% by weight
Mg: 0.3% to 0.8% by weight
Cr: 0.05% to 0.35% by weight
Fe: <0.18% by weight
Mn: <0.06% by weight
Ti: <0.16% by weight
Cu: 0.006-0.015% by weight
Sr: 0.010 to 0.030% by weight
Zr<0.006% by weight
Zn<0.006% by weight
Impurities: <0.1% by weight
and is supplemented by Al to an extent of 100% by weight in each case.

Such an Al casting alloy is stronger, tougher and more ductile compared to the prior art.

The inventive selection of alloy constituents in the order of magnitude specified leads to a further significant improvement in the mechanical properties which is already apparent in the cast state, but especially in a cast component after a 2-stage heat treatment, namely a solution annealing operation and a subsequent age hardening operation, with preferable provision of quenching of the cast component in water between these two heat treatment steps. For chassis applications, preferably for wheel-bearing components, very preferably for damper stilts, wheel bearings and especially swivel bearings, but also for control arms, the result is an overall increase in mechanical indices.

Entirely unexpectedly, especially in relation to the mechanical index of elongation at break A5, it has been found that the upper limit specified as critical for copper in DE 10 2013 108 127 A1 of 0.006% by weight is exceeded in a manner essential to the invention.

For optimization of the mechanical indices, it may be advantageous when Cu is present with a content of more than 0.006% by weight, preferably of more than 0.007% by weight, more preferably of more than 0.008% by weight, most preferably at least 0.009% by weight. For optimization of the mechanical indices, it may be advantageous when Cu is present with a content of less than 0.015% by weight, preferably of less than 0.013% by weight, more preferably of less than 0.012% by weight, most preferably of less than 0.011% by weight.

The alloys of the invention may contain impurities resulting from the preparation, for example Pb, Ni, etc., as is common knowledge to the person skilled in the art.

For optimization of the mechanical indices, it may be advantageous when Si is present with a content of more than 3.1% by weight, preferably of more than 3.3% by weight, more preferably of more than 3.4% by weight. For optimization of the mechanical indices, it may be advantageous when Si is present with a content of less than 3.7% by weight, preferably of less than 3.5% by weight.

It may be advantageous for particular applications when Si is present with a content of more than 3.3% to less than 3.7% by weight. For some other applications, it may be advantageous when Si is present with a content of more than 3.0% to less than 3.3% by weight.

For optimization of the mechanical indices, it may be advantageous when Mg is present with a content of more than 0.40% by weight, preferably of more than 0.50% by weight, more preferably of more than 0.55% by weight. For optimization of the mechanical indices, it may be advantageous when Mg is present with a content of less than 0.70% by weight, preferably of less 0.60% by weight.

For optimization of the mechanical indices, it may be advantageous when Cr is present with a content of more than 0.10% by weight, preferably of more than 0.15% by weight, more preferably of more than 0.20% by weight, most preferably of more than 0.25% by weight. For optimization of the mechanical indices, it may be advantageous when Cr is present with a content of at most 0.30% by weight, preferably of less than 0.30% by weight.

For optimization of the mechanical indices, it may be advantageous when Fe is present with a content of more than 0.01% by weight, preferably of more than 0.05% by weight, more preferably of more than 0.07% by weight. For optimization of the mechanical indices, it may be advantageous when Fe is present with a content of less than 0.15% by weight, preferably of less than 0.12% by weight.

For optimization of the mechanical indices, it may be advantageous when Mn is present with a content of more than 0.01% by weight, preferably of more than 0.02% by weight. For optimization of the mechanical indices, it may be advantageous when Mn is present with a content less than 0.15% by weight, preferably of less than 0.12% by weight, more preferably of less than 0.10% by weight.

For optimization of the mechanical indices, it may be advantageous when Ti is present with a content of more than 0.01% by weight, preferably of more than 0.03% by weight, more preferably of more than 0.04% by weight. For optimization of the mechanical indices, it may be advantageous when Ti is present with a content of less than 0.10% by weight, preferably of less than 0.08% by weight, more preferably of less than 0.065% by weight, most preferably of less than 0.055% by weight.

For optimization of the mechanical indices, it may be advantageous when Sr is present with a content of more than 0.015% by weight, preferably of more than 0.020% by weight. For optimization of the mechanical indices, it may be advantageous when Sr is present with a content of less than 0.030% by weight, preferably of less than 0.025% by weight.

For optimization of the mechanical indices, it may be advantageous when Zr is present with a content of more than 0.001% by weight. For optimization of the mechanical indices, it may be advantageous when Zr is present with a content of less than 0.005% by weight, preferably of less than 0.004% by weight, more preferably of less than 0.003% by weight.

For optimization of the mechanical indices, it may be advantageous when Zn is present with a content of more than 0.001% by weight, preferably of more than 0.002% by weight. For optimization of the mechanical indices, it may be advantageous when Zn is present with a content of less than 0.005% by weight, preferably of less than 0.004% by weight.

For numerous applications, it may be advantageous when impurities are present with a content of less than 0.05% by weight, preferably less than 0.035% by weight.

For certain cast components, it has been found to be advantageous when the Al casting alloy of the invention is a low-pressure casting Al alloy.

Accordingly, the invention also relates to a method of producing a cast component from an Al casting alloy as claimed in any of claims 1 to 22, in which the low-pressure casting method is employed.

For particular cast components, it has been found to be advantageous when the Al casting alloy is a counterpressure casting (CPC) Al alloy.

Accordingly, the invention also relates to a method of producing a cast component from an Al casting alloy as claimed in any of claims 1 to 22, in which the low-pressure counterpressure casting method is employed.

Various permanent mold casting methods are suitable in principle as manufacturing methods for cast components, especially as chassis parts, preferably as wheel-bearing components, very preferably as damper stilts, wheel bearings or swivel bearings, of motor vehicles made from the cast alloy of the invention. Owing to the very good mechanical properties in the case of highly stressed wheel-bearing parts of motor vehicles, however, particularly low-pressure diecasting and the counterpressure casting (CPC) method, which is also referred to as the counterpressure diecasting method, are suitable as manufacturing methods.

Manufacturing methods employed for cast components, especially as chassis parts, preferably as wheel-bearing components, very preferably as damper stilts, wheel bearings or swivel bearings, of motor vehicles made from the cast alloy of the invention may advantageously be squeeze-casting, gravity diecasting or pressure diecasting, especially thixocasting, rheocasting or low-pressure sand casting.

In order to achieve or even further develop the abovementioned advantages, it is advantageous when the cast components are subjected to a two-stage heat treatment, namely a solution annealing operation and a subsequent age hardening operation. It may be advantageous when the cast component is quenched in water between the two heat treatment stages.

It may be appropriate when the cast component after the casting operation is solution-annealed between 530° C. and 550° C. for 6 to 10 h, preferably between 540° C. and 550° C. for 7 to 9 h, especially for 8 to 9 h, most preferably between more than 540° C. and 550° C. for 7 to 9 h, especially for 8 to 9 h.

It may be appropriate when the cast component after the casting operation is tempered between 180° C. and 210° C. for 1 to 8 h, especially for 1 to 6.5 h, preferably between 180° C. and 190° C. for 1 to 6.5 h, especially for 4 to 6.5 h, more preferably between 180° C. and less than 190° C. for 4 to 6.5 h, especially for 5 to 6.5 h.

The invention further provides for the use of an Al casting alloy as claimed in any of the claims or of a cast component, especially one that has been heat-treated, as claimed in any of the claims for chassis parts of motor vehicles, preferably for wheel-bearing components of motor vehicles, most preferably for damper stilts, wheel bearings or swivel bearings of motor vehicles.

According to the invention, the cast components have an improved strength/strain ratio coupled with improved microstructure properties. The casting method firstly enables a casting free of larger defects, known as craters; secondly, the microstructure is positively affected in such a way that the number of inner indentations that reduce elongation at break is kept to a minimum.

As already mentioned, the Al casting alloy of the invention has been found to be especially suitable particularly for components under relatively high stress, such as damper stilts, wheel bearings or swivel bearings. A very preferred process for production of such relatively highly stressed components is the counterpressure diecasting (CPC) method.

Cast components of the invention that have been produced from an Al casting alloy as claimed in any of the claims and/or by a method as claimed in any of the claims feature, after a heat treatment, a yield point R_P0.2 of 300 to 330 MPa, preferably of >320 to 330 MPa, and/or an elongation at break A5 of 7% to 11%, preferably of 8.5% to 10%, more preferably of 9% to 9.5%, and/or a tensile strength R_m of 350-375 MPa, preferably of >360-375 MPa.

EXAMPLE

To ascertain the mechanical properties of an alloy of the invention containing 3.4% by weight of Si, 0.6% by weight of Mg, 0.27% by weight of Cr, 0.09% by weight of Fe, 0.03% by weight of Mn, 0.05% by weight of Ti, 0.009% by weight of Cu, 0.022% by weight of Sr, 0.002% by weight of Zr, 0.003% by weight of Zn and impurities of less than 0.1% by weight, in each case supplemented to 100% by weight with Al, what is called a “French tensile specimen” according to DIN 50125 is cut out of a swivel bearing produced by means of a counterpressure diecasting (CPC) method, the swivel bearing having received a heat treatment (solution annealing at 540° C. for 8 h, quenching in water, age hardening at 180° C. for 6.5 h) beforehand. The casting of comparative examples (AlSi3Mg0.5 and AlSi3Mg0.5Cr0.3) and subsequent heat treatment are effected under the same conditions. The alloys to be compared differ solely in the chromium content. The specimen is taken at the same position in the swivel bearing. The mechanical properties of tensile strength R_m, yield point R_p0.2 and elongation at break A5 according to DIN10002 are ascertained.

	Rm [MPa]	Rp0.2 [MPa]	A5 [%]
	AlSi3Mg0.5	327	263	9.3
	Alloy of the invention	369	322	9.12
	AlSi3Mg0.5Cr0.3	358	308	6.9

Against the background of DE 10 2013 108 127 A1 and the upper limit for copper of 0.006% by weight which is specified as critical for the mechanical indices, the achievement of the abovementioned mechanical indices for the alloy of the invention was not to be expected.

Claims

1. An Al casting alloy containing at least five of the following alloy constituents:

Si: 3.0% to 3.8% by weight

Mg: 0.3% to 0.8% by weight

Cr: 0.05% to 0.35% by weight

Fe: <0.18% by weight

Mn: <0.06% by weight

Ti: <0.16% by weight

Cu: 0.006-0.015% by weight

Sr: 0.010% to 0.030% by weight

Zr<0.006% by weight

Zn<0.006% by weight

Impurities: <0.1% by weight

and is supplemented by Al to an extent of 100% by weight in each case.

2. The Al casting alloy as claimed in claim 1, wherein Si is present with a content of more than 3.1% by weight, preferably of more than 3.3% by weight, more preferably of more than 3.4% by weight.

3. The Al casting alloy as claimed in claim 1, wherein Si is present with a content of less than 3.7% by weight, preferably of less than 3.5% by weight.

4. The Al casting alloy as claimed in claim 1, wherein Mg is present with a content of more than 0.40% by weight, preferably of more than 0.50% by weight, more preferably of more than 0.55% by weight.

5. The Al casting alloy as claimed in claim 1, wherein Mg is present with a content of less than 0.70% by weight, preferably of less 0.60% by weight.

6. The Al casting alloy as claimed in claim 1, wherein Cr is present with a content of more than 0.10% by weight, preferably of more than 0.15% by weight, more preferably of more than 0.20% by weight, most preferably of more than 0.25% by weight.

7. The Al casting alloy as claimed in claim 1, wherein Cr is present with a content of at most 0.30% by weight, preferably of less than 0.30% by weight.

8. The Al casting alloy as claimed in claim 1, wherein Fe is present with a content of more than 0.01% by weight, preferably of more than 0.05% by weight, more preferably of more than 0.07% by weight.

9. The Al casting alloy as claimed claim 1, wherein Fe is present with a content of less than 0.15% by weight, preferably of less than 0.12% by weight.

10. The Al casting alloy as claimed in claim 1, wherein Mn is present with a content of more than 0.01% by weight, preferably of more than 0.02% by weight.

11. The Al casting alloy as claimed in claim 1, wherein Mn is present with a content less than 0.15% by weight, preferably of less than 0.12% by weight, more preferably of less than 0.10% by weight.

12. The Al casting alloy as claimed in claim 1, wherein Ti is present with a content of more than 0.01% by weight, preferably of more than 0.03% by weight, more preferably of more than 0.04% by weight.

13. The Al casting alloy as claimed in claim 1, wherein Ti is present with a content of less than 0.10% by weight, preferably of less than 0.08% by weight, more preferably of less than 0.065% by weight, most preferably of less than 0.055% by weight.

14. The Al casting alloy as claimed in claim 1, wherein Cu is present with a content of more than 0.006% by weight, preferably of more than 0.007% by weight, more preferably of more than 0.008% by weight, most preferably at least 0.009% by weight.

15. The Al casting alloy as claimed in claim 1, wherein Cu is present with a content of less than 0.015% by weight, preferably of less than 0.013% by weight, more preferably of less than 0.012% by weight, most preferably of less than 0.011% by weight.

16. The Al casting alloy as claimed in claim 1, wherein Sr is present with a content of more than 0.015% by weight, preferably of more than 0.020% by weight.

17. The Al casting alloy as claimed in claim 1, wherein Sr is present with a content of less than 0.030% by weight, preferably of less than 0.025% by weight.

18. The Al casting alloy as claimed in claim 1, wherein Zr is present with a content of more than 0.001% by weight.

19. The Al casting alloy as claimed in claim 1, wherein Zr is present with a content of less than 0.005% by weight, preferably of less than 0.004% by weight, more preferably of less than 0.003% by weight.

20. The Al casting alloy as claimed in claim 1, wherein Zn is present with a content of more than 0.001% by weight, preferably of more than 0.002% by weight.

21. The Al casting alloy as claimed in claim 1, wherein Zn is present with a content of less than 0.005% by weight, preferably of less than 0.004% by weight.

22. The Al casting alloy as claimed in claim 1, wherein impurities are present with a content of less than 0.05% by weight, preferably less than 0.035% by weight.

23-32. (canceled)

33. A cast component produced from an Al casting alloy as claimed in claim 1, wherein the cast component after a heat treatment has a yield point RP0.2 of 300 to 330 MPa, preferably of >320 to 330 MPa, and/or an elongation at break A5 of 7% to 11%, preferably of 8.5% to 10%, more preferably of 9% to 9.5%, and/or a tensile strength Rm of 350-375 MPa, preferably of >360-375 MPa.