ALUMINUM ALLOY, COMPONENT OF ALUMINUM ALLOY AND METHOD OF PRODUCING A COMPONENT FROM ALUMINUM ALLOY

Abstract

The invention relates to an aluminum-silicon casting alloy which, in addition to aluminum and unavoidable impurities, comprises at least the following alloying constituents:

Description

The invention relates to an aluminum alloy for die casting, a die cast aluminum alloy component, and a die casting method for producing an aluminum alloy component.

Die casting is an economical process for the series production of components, for example for motor vehicles. In the case of structural components for motor vehicles, low weight and low unit costs are desired on the one hand, while on the other hand there are high requirements for the ductility of the material and the energy absorption capacity of the finished component. The energy absorption capacity of the finished component is of particular importance for components that are to deform in the event of a crash. The aluminum alloys suitable for this purpose are also known as crash alloys. In addition, the material should be reliably processable and permit high series production quality with the lowest possible mold shrinkage and the least possible reworking of the cast structural components.

Structural components for the automotive industry are becoming steadily larger and more complex due to component and function integration. Dispensing with the heat treatment and possible straightening processes of these thin-walled but large-area components brings a significant cost advantage for automotive production. This advantage applies in particular to battery boxes for hybrid and electric vehicles. Battery boxes are integrated into the vehicle's support structure and have to share the loads in the event of a crash.

Therefore, an aluminum casting alloy is sought that is suitable for the production of structural components for the automotive industry, which should have good crash properties, using the die casting process.

According to the invention, this objective is achieved with an aluminum-silicon casting alloy according to claim 1 which, in addition to at least 88% by weight of aluminum, comprises the following alloying constituents:

Silicon   between 6.0 and 8.5% by weight
Zinc      between 0.2 and 0.8% by weight
Manganese between 0.2 and 0.6% by weight
Chromium  between 0.1 and 0.3% by weight and
Magnesium with up to 0.05% by weight.

Preferably, the silicon content of the aluminum-silicon casting alloy is between 7.0 and 8.5% by weight, and particularly preferably between 7.5 and 8.5% by weight.

Preferably, the alloy comprises one or more of the following alloying components:

Strontium between 0.01 and 0.02% by weight and
Titanium  between 0.04 and 0.15% by weight

Other alloy components can be

Iron   with up to 0.2% by weight,
Copper with up to 0.5% by weight, preferably up to 0.2% by
       weight

and/or

• • Molybdenum and/or zirconium with together up to 0.25% by weight.

Preferably, the magnesium content is not more than 0.01% by weight.

In addition, the aluminum-silicon casting alloy may contain up to 0.15% by weight of hafnium, cerium, lanthanum, and/or other rare earth element.

The rest are respectively aluminum and usual accompanying elements.

The aluminum-silicon casting alloy AlSi8ZnMn according to the invention is suitable for producing structural components with good crash properties by die casting, for example for the automotive industry. The components produced with the aluminum-silicon casting alloy according to the invention do not require any heat treatment after the die casting process to achieve high ductility and high energy absorption capacity. Die-cast components made from the aluminum-silicon casting alloy according to the invention exhibit good folding behavior and can thus be used as crash-relevant components.

Previously known casting alloys for components with good crash properties either require heat treatment, e.g. solution annealing (see DIN EN 1706 EN-AC-43500,) or are difficult to cast by die casting (see DIN EN 1706 EN-AC-51500, AlMg5Si2Mn). The aluminum-silicon casting alloy AlSi8ZnMn according to the invention can be cast well in die casting due to its silicon content. The flowability, mold filling and demoldability are comparable to EN-AC-43500 and AlSi9Mn materials used in series production.

Die casting alloys that require solution annealing after casting are usually cast by means of Vacural casting—i.e. by means of a vacuum die casting process-because classic die casting machines are subject to the risk of bubble formation (blister risk), making them unsuitable for solution annealing.

The standard crash alloys are alloys that require solution annealing and are therefore not cast on “classic” die casting machines.

The aluminum-silicon casting alloy according to the invention achieves the desired properties in terms of ductility of the material and energy absorption capacity of the finished component even without solution annealing, so that structural components produced by means of the aluminum-silicon casting alloy according to the invention can be supplied to their final use, e.g. as a component of a vehicle, without the component having to be solution annealed between die casting and installation in the vehicle.

The aluminum-silicon casting alloy according to the invention is very ductile due to its very low iron and manganese content and exhibits a bending angle of greater than 60°.

If the aluminum-silicon casting alloy according to the invention contains at least 0.05 wt. % molybdenum according to a preferred variant, the yield strength R_p0,2 and the elongation at fracture A are increased by the solid solution strengthening of zinc, titanium and molybdenum in the aluminum-silicon system.

Manganese and chromium are used to ensure the demoldability of the components from the die-casting mold despite the low silicon and iron content.

Limiting the magnesium content to a maximum of 0.05% by weight, preferably to a maximum of 0.01% by weight, has also proved advantageous.

According to the invention, a method for producing a structural component, in particular for a motor vehicle, is also proposed, characterized in that the structural component is cast using the aluminum-silicon casting alloy according to the invention, preferably in a die casting process.

Preferably, the die is tempered to a temperature between 105° C. and 290° C. before casting, and the melt of the aluminum-silicon casting alloy according to the invention preferably has a temperature between 690° C. and 725° C. immediately before casting. This means that the melt is about 10° C. to 20° C. hotter than in conventional die casting processes using, for example, the aluminum-silicon casting alloy AlSi10MnMg. The casting mold, on the other hand, is somewhat colder than usual up to this point.

Preferably, no solution annealing takes place between die casting and final use of the component. Whereas solution annealing is necessary in conventional components that deform in the event of a crash in order to improve the energy absorption capacity, a component made from the aluminum-silicon casting alloy according to the invention does not require solution annealing—on the contrary, solution annealing could tend to worsen the properties. The manufacture of components from the aluminum-silicon casting alloy according to the invention is thus more economical and the properties obtained are better.

According to the invention, a component, in particular a structural component preferably for a motor vehicle, made from the aluminum-silicon casting alloy according to the invention is also proposed. The structural component is preferably a battery housing for a hybrid or a purely electric vehicle. The component is preferably not solution annealed.

With the aluminum-silicon casting alloy according to the invention and structural components made from it-the following advantages can be achieved:

• • The aluminum-silicon casting alloy according to the invention is a die casting alloy with good castability, mold filling and flowability.
  • The aluminum-silicon casting alloy according to the invention has high ductility without heat treatment of the castings.
  • The aluminum-silicon casting alloy according to the invention is suitable for the die casting production of structural components.
  • The very high ductility of the aluminum-silicon casting alloy according to the invention and a high energy absorption capacity allow its use for crash-relevant components.
  • The aluminum-silicon casting alloy according to the invention is suitable for the die casting of structural components, in particular battery housings for electric and hybrid vehicles.
  • The aluminum-silicon casting alloy according to the invention is suitable for the die casting of large components with shot weights >25 kg due to its high flowability and low tendency to stick in die casting.
  • The aluminum-silicon casting alloy according to the invention is directly transferable to existing die casting processes as an AlSi alloy system.
  • The aluminum-silicon casting alloy according to the invention has a low tendency to stick in die casting molds due to the combination of Mn, Cr and Mo in the Al-Si system.
  • The die cast components made from the aluminum-silicon casting alloy according to the invention are suitable for industrial joining processes, in particular also for self-pierce riveting, also with sheets, profiles and other materials.

EXAMPLES AND TEST RESULTS

An exemplary aluminum-silicon casting alloy according to the invention is reflected in the following table:

TABLE 1
Main alloy range of an alloy according
to the invention AlSi8ZnMn
		Si	Fe	Cu	Mn	Mg	Cr	Zn
	min	6.5	—	—	0.2	—	0.1	0.2
	max	8.5	0.2	0.5	0.6	0.01	0.3	0.8
	Sr	Ti	Zr or Mo
min	0.01	0.04	—	Rest aluminum and usual
max	0.02	0.15	0.25	accompanying elements

Table 2 (in the appendix) lists various materials and their properties.

The materials were manufactured and cast into gravity die casted specimens for round tensile bars. The tension bars were used to determine the mechanical (mecha.) properties as well as the bending angle. All results are for separately cast permanent mold specimens in the F condition (as-cast condition, without heat treatment). The elements of the alloys in round brackets were varied in the tests to quantify their influence. Table 2 shows that the bending angle of the newly developed materials was almost doubled compared to the existing materials. The two materials highlighted in gray were used for more extensive die casting tests and crash tests.

For die casting tests, 240 kg of each of the two materials shown in italics in Table 2 (see Annex) were produced and cast into structural components in the form of a profile. The die casting tests show very good castability with low iron and manganese content of the alloys and good mechanical properties. In a passed crash test on the drop tower test rig, it was determined that the first fold of the profile remained crack-free for 5 ms. It is required that the structural component remains crack-free for at least 3.5 ms.

The die casting tests were accompanied by permanent mold casting tests to determine the notched impact strength as a measure of the energy absorption behavior of the component.

It is noticeable that the notched impact strength of the test alloys could be increased by more than four times compared to conventional aluminum die casting alloys in condition F. The components made of these alloys do not require any heat treatment. The components made from these materials do not require heat treatment.

TABLE 3
Comparison of impact strength with mechanical properties
of the two test alloys (see Table 2) above and a conventional
aluminum die casting alloy below:
				Notched
Rp0.2	Rm	A	BW	impact strength
in MPa	in MPa	in %	in °	in kJ/m2
AlSi8ZnMnMo(Cr, Fe)
77.4 ± 0.7	178.5 ± 3.9	13.9 ± 3.9	53.3 ± 6.5	415.65 ± 61.29
AlSi8ZnMnMo(Zr)
77.3 ± 1.14	180.0 ± 2.38	20.7 ± 1.9	63 ± 2.38	463.0 ± 50.2
Conventional aluminum die casting alloy
102.8 ± 0.5	205.0 ± 1.2	4.8 ± 0.3	17.4 ± 4.3	107.4 ± 16.9*

The die casting tests of the sample structural components showed that both materials shown in italics in Table 2 achieved a yield strength of approx. 105 MPa. By adding zinc (Zn) and titanium (Ti), the yield strength could be further increased. Ti was found to have a significant and Zn a minor effect on solid solution strengthening in gravity die casting.

FIG. 1 shows the yield strength R_p0,2 and the elongation at fracture A of eight investigated alloys with different zinc and titanium contents with two newly developed variants named Milestone 4. Milestone 4 aimed to raise the yield strength and maintain the elongation at fracture at >14% while limiting the use of peritectic elements to avoid the formation of undesirable intermetallic phases. The “Milestone 4” results in FIG. 2 surprisingly showed that these goals could be achieved with two materials.

The analyses of the “Milestone 4” materials in FIG. 1 are listed in Table 4 (in the appendix) and designated according to the sequence as AlSi8Zn0.6Mn0.35Zr and AlSi8Zn0.4Mn0.35Cr. The alloys are already very ductile in gravity die casting without heat treatment. Experience shows that the strengths increase significantly in die casting, while the elongation at fracture remains roughly constant, making them suitable as naturally ductile casting alloys for structural components, in particular battery boxes for electric vehicles with crash properties.

TABLE 2
Analysis and mechanical properties of known alloys and alloys according to the
invention. Mechanical properties (yield strength Rp0.2, tensile strength Rm, elongation
at break A25) determined on separately cast permanent mold specimens. Bending
angles (BW) apply with respect to components with 2 mm wall thickness.
	Element content in % by weight
Alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	P
AlSi6MnZnZrMo(Ce)	6.06	0.062	0.00012	0.301	0.0011	0.00063	0.409	0.075	0.0034
	6.35	0.029	0.00086	0.305	0.0016	0.00066	0.395	0.067	0.0032
	6.29	0.03	0.0004	0.301	0.0014	0.00069	0.391	0.067	0.0029
	6.09	0.034	0.0031	0.3	0.0033	0.00076	0.407	0.067	0.0031
	6.63	0.127	0.00034	0.305	0.0011	0.00077	0.394	0.06	0.0025
AlSi6—10ZnMnMo(Zr, V)	6.06	0.028	0.00005	0.301	0.0007	0.00063	0.409	0.052	0.0039
	8.09	0.028	0.00005	0.296	0.0007	0.00064	0.408	0.052	0.0039
	8.99	0.028	0.00008	0.301	0.00071	0.00064	0.404	0.053	0.0042
	10.09	0.031	0.00004	0.304	0.00067	0.00062	0.405	0.052	0.0043
	9.87	0.037	0.00004	0.295	0.00077	0.00078	0.425	0.048	0.0038
AlSi8ZnMnMo(Cr, Fe, Zr)	8.00	0.033	0.00002	0.301	0.00029	0.00059	0.398	0.063	0.0032
	8.16	0.038	0.00012	0.302	0.00083	0.249	0.409	0.065	0.0026
	8.24	0.104	0.00057	0.3	0.00081	0.245	0.408	0.064	0.0028
	8.09	0.106	0.00053	0.296	0.0014	0.242	0.407	0.063	0.0027
	mech. properties
	Rp0.2	Rm
	Element content in % by weight	in	in	A25	BW
	Alloy	V	Sr	Zr	Mo	Ce	Mpa	MPa	in %	in °
	AlSi6MnZnZrMo(Ce)	0.0052	0.019	0.207	0.126	max.	73.7	175.5	19.9	60.4
		0.0034	0.02	0.217	0.134	0.03	69.3	170.0	18.3	49.8
		0.0034	0.018	0.215	0.132		73.5	175.0	19.3	55.6
		0.0034	0.02	0.204	0.131		69.0	173.0	15.9	43.0
		0.0041	0.017	0.205	0.132		74.8	177.0	16.3	52.8
						Hf
	AlSi6—10ZnMnMo(Zr, V)	0.0037	0.019	0.258	0.134	max.	73.8	175.3	20.7	67.6
		0.0037	0.019	0.258	0.134	0.15	77.3	180.0	20.7	63.1
		0.0037	0.02	0.249	0.133		85.6	190.8	14.9	59.6
		0.0037	0.023	0.249	0.132		84.5	187.0	15.0	52.4
		0.113	0.024	0.243	0.117		88.8	190.8	9.1	47.6
	AlSi8ZnMnMo(Cr, Fe, Zr)	0.004	0.02	0.00064	0.14		73.0	175.8	20.1	60.5
		0.0042	0.017	0.00065	0.138		77.4	181.0	18.1	51.6
		0.0042	0.02	0.00068	0.137		77.4	178.5	13.9	53.3
		0.0041	0.019	0.26	0.137		84.8	182.0	10.4	46.2

TABLE 4
Analysis of materials according to the invention and mechanical properties of the materials in die casting
	mech. properties
	Rp0.2	Rm
	Element content in % by weight	in	in	A25	BW
Alloy	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	P	V	Sr	Zr	Mo	Ce	Mpa	MPa	in %	in °
AlSi8Zn0.6Mn0.35Zr	8.2	0.11	0.040	0.36	0.001	0.12	0.63	0.12	<0.001	—	0.018	0.17	—	—	115	250	15	42
AlSi8Zn0.4Mn0.35Cr	8.0	0.09	0.001	0.36	0.001	0.23	0.39	0.05	<0.001	—	0.019	—	0.14	—	120	26	13	40
AlSi7Zn0.6Mn0.35Zr	7.2	0.2	0.05	0.52	0.001	0.12	0.63	0.12	<0.001	—	0.017	0.15	—	—	125	270	10	32
AlSi7Zn0.4Mn0.35Cr	7.0	0.15	0.50	0.40	0.001	0.20	0.40	0.05	<0.001	—	0.019	—	0.14	—	140	280	8	30

Claims

1. An aluminum-silicon casting alloy comprising, in addition to aluminum and unavoidable impurities, at least the following alloying constituents:

2. The aluminum-silicon casting alloy according to claim 1, comprising between 0.01 and 0.02% by weight of strontium.

3. The aluminum-silicon casting alloy according to claim 1, comprising between 0.04 and 0.15% by weight of titanium.

4. The aluminum-silicon casting alloy according to claim 1, comprising up to 0.2% by weight of iron.

5. The aluminum-silicon casting alloy according to claim 1, comprising up to 0.5% by weight of copper.

6. The aluminum-silicon casting alloy according to claim 1, comprising up to 0.01 % by weight of magnesium.

7. The aluminum-silicon casting alloy according to claim 1, comprising up to 0.25% by weight of molybdenum and/or zirconium.

8. The aluminum-silicon casting alloy according to claim 1, comprising up to 0.15 % by weight of hafnium, cerium and/or another rare earth element.

9. A structural component, in particular for a motor vehicle, wherein the structural component is cast from an aluminum-silicon casting alloy according to claim 1.

10. The structural component according to claim 9, wherein the finished structural component is not solution annealed.

11. The stuctural component according to claim 9, wherein the structural component is a battery housing for a hybrid or electric vehicle.

12. A method of producing a component, in particular a structural component preferably for a motor vehicle, wherein the component is cast using the aluminum-silicon casting alloy according to claim 1.

13. The method according to claim 12, wherein the component is cast in a die casting process.

14. The method according to claim 13, wherein for die casting a die casting mold is used which is tempered to a temperature between 105° C. and 290° C. before casting.

15. The method according to claim 13, wherein the melt of the aluminum-silicon casting alloy has a temperature between 690° C. to 725° C. immediately before casting.

16. The method according to claim 13, wherein no solution annealing takes place between the die casting and a final use of the component.