WO2023099520A1

WO2023099520A1 - Aluminum die casting alloy

Info

Publication number: WO2023099520A1
Application number: PCT/EP2022/083766
Authority: WO
Inventors: Marc Hummel; Steffen Otterbach; Marius KOHLHEPP
Original assignee: Audi Ag
Priority date: 2021-12-03
Filing date: 2022-11-30
Publication date: 2023-06-08
Also published as: DE102021131935A1

Abstract

The invention relates to an aluminum die casting alloy having the following alloy constituents: 5 to 9 wt. %, in particular 6.5 to 8 wt. %, silicon, 0.05 to 0.3 wt. %, in particular 0.1 to 0.2 wt. %, nickel, manganese and/or chromium and/or molybdenum and/or vanadium, the sum of said elements being 0.05 to 1.0 wt. %, in particular 0.2 to 0.6 wt. %, the remainder consisting of aluminum and inevitable impurities.

Description

Die-cast aluminum alloy

DESCRIPTION:

The invention relates to an aluminum die-cast alloy, a method for the heat treatment of a component made from an aluminum die-cast alloy, and a component for a motor vehicle.

EP 1 443 122 B1 discloses an aluminum alloy for die-casting components with high elongation in the cast state. Further compositions for die-cast aluminum alloys are described in EP 1 719 820 A2, DE 10 2006 039 684 B4, DE 10 2010 055 011 A1 or DE 10 2019 205 267 B3.

DE 102005 037 738 A1 describes an aluminum cast alloy containing silicon, magnesium, iron, copper, zinc, manganese, titanium, zirconium, nickel and cobalt.

An aluminum-silicon cast alloy is known from EP 1 978 120 A1, which additionally contains, inter alia, magnesium, titanium, zirconium, manganese, iron, copper and nickel.

A hardenable aluminum cast alloy with silicon, magnesium, nickel and cobalt is described in DE 100 62 547 A1.

WO 2009/106327 A1 discloses a method for heat treatment and coating of a component and a component produced using the method. EP 2 138 593 A2 discloses a method for producing a cast component from an aluminum die-cast alloy, in which the cast component is subjected to a heat treatment process after casting, using an aluminum die-cast alloy.

DE 10 2016 118 729 A1 discloses copper-free aluminum alloys suitable for high-pressure casting, which can be subjected to hardening at elevated temperatures.

CH 168202 A discloses an aluminum alloy containing 8 to 15% silicon, 0.1 to 0.6% magnesium and also 1% of at least one alloy component responsible for increasing the fatigue strength.

GB 595,531 A discloses an aluminium-based alloy with excellent castability.

US 2005/0224145 A1 discloses castings made from an aluminum alloy which are exposed to high thermal and mechanical loads.

The alloy compositions known from these documents are used for engine components such as crankcases, cylinder heads and possibly pistons.

In principle, the prior art therefore provides a large number of aluminum die-casting alloys with numerous compositions and heat treatments for the production of structural components. However, due to the trend towards large structural cast components, many of these are no longer an option.

The best combination of strength and ductility can be achieved with heat treatable aluminum alloys in the T6 temper, making them very attractive both in terms of lightweight potential and for use in joining processes such as semi-tubular punch riveting. Depending on whether the If the desired increase in strength is only achieved by solid solution hardening and strain hardening or additionally by precipitation hardening, a distinction is made between hardenable and naturally hard, ie non-hardenable alloys. The naturally hard alloys are, for example, of the AIMg, AIMn, AIMgMn and AlSi type. The hardenable alloys are, for example, of the AICuMg, AICuSiMn, AISiMg, AIZnMg and AIZnMgCu type. Disadvantages of large-area structural cast components, however, are the distortion during heat treatment, which leads to poor dimensional accuracy, as well as the high costs for heat treatment due to the low packing density and the associated space requirement due to large furnace systems.

Another option is heat treatment in the T5 condition, which, among other things, can be carried out very cost-effectively through the painting process and therefore does not require any subsequent heat treatment. The dimensional accuracy is not affected by the elimination of solution annealing. In addition, production is streamlined due to the elimination of furnace systems. However, achieving high strength in the painting process is challenging, since the trend towards lower temperatures and shorter times for the purpose of energy saving and sustainability offers a very low curing potential for structural components. However, a combination of magnesium and a higher copper content or a subsequent T5 heat treatment is often required to achieve high strength. However, the use of a high copper content makes the alloy susceptible to corrosion. Furthermore, copper leads to embrittlement of the material and reduces weldability due to an increased tendency to hot cracking. In the case of T5 alloys without copper, only magnesium is used as an alloy component, which means that only moderately high strengths can be achieved. A subsequent T5 heat treatment, on the other hand, puts the cost advantage compared to the T6 alloy into perspective, since a furnace system is also required. In addition, joining operations must then be carried out in the already hardened state, which makes them more difficult. Another possibility is to use naturally hard alloys. However, these can only achieve limited strength and therefore have a very limited potential for lightweight construction.

It is therefore an object of the present invention to create an aluminum die-cast alloy and a method for heat treatment of a component for a motor vehicle made from a hardenable aluminum die-cast alloy, from which components with high strength and high ductility and the lowest possible distortion are produced can.

According to the invention, this object is achieved by the features mentioned in claim 1.

The die-cast aluminum alloy according to the invention, which contains 5 to 9% by weight, in particular 6.5 to 8% by weight, silicon as alloy components; 0.05 to 0.3% by weight, in particular 0.1 to 0.2% by weight, nickel; Manganese and/or chromium and/or molybdenum and/or vanadium, the sum of these elements being 0.05 to 1.0% by weight, in particular 0.2 to 0.6% by weight, with the remainder being aluminum and unavoidable impurities, has a particularly good ratio of strength and ductility in the as-cast state after casting, which ensures excellent joinability. The alloy combination according to the invention, which combines good castability, an advantageous relationship between strength and ductility, as well as good joinability in the cast state and high hardening in the T5 state, forms an ideal basis for use in large-area and/or large-volume, particularly thin-walled, Structural cast components created. Strontium, titanium, zirconium, magnesium, copper and/or zinc with the proportions described below are optionally provided in the die-cast aluminum alloy according to the invention.

The silicon content, which is reduced compared to the usual aluminium-silicon die-casting alloys for structural cast parts, ensures a good balance between strength and ductility in the cast state. the diminished Castability due to the reduction of the silicon is counteracted according to the invention by the addition of nickel. Surprisingly, this effect is only evident in the range between 0.05 to 0.3%, in particular 0.1 to 0.2% nickel. In addition, the strength in the as-cast state is increased by the use of nickel, as long as the proportion does not exceed 0.3%, in particular 0.2%, without impairing the ductility. However, the ductility drops very sharply at higher levels. In addition, nickel also acts against mold sticking, which means that the proportion of manganese can be reduced, which in turn improves ductility.

The elements manganese and/or chromium and/or molybdenum and/or vanadium are added to reduce mold sticking, and their proportion can be significantly reduced through the use of nickel as described above, so that the sum of these elements is 0.05 to 1.0 wt %, in particular 0.2 to 0.6% by weight.

In a very advantageous development of the die-cast aluminum alloy, it can contain 0.008 to 0.025% by weight, in particular 0.01 to 0.02% by weight, of strontium. The addition of strontium results in a refinement or refining of the silicon structure.

In a further advantageous development of the die-cast aluminum alloy, it can contain 0.05 to 0.2% by weight, in particular 0.11 to 0.18% by weight, of titanium.

Alternatively or additionally, the aluminum die-cast alloy according to the invention can have 0.05 to 0.15% by weight, in particular 0.05 to 0.10% by weight, of zirconium.

Zirconium and titanium have a grain-refining effect and form intermetallic phases and precipitations in the structure. This increases strength as cast without affecting ductility and joinability. This is particularly the case when zirconium and titanium are used together. Surprisingly, there is an excess of titanium in the Ratio of titanium to zirconium proven to be particularly effective. In contrast to known solutions, in which titanium contents of 0.05 to 0.10% and higher zirconium contents of 0.15 to 0.30% are used, a proportion of 0.18% titanium and 0. 06% zirconium is particularly effective, as both strength and ductility increase and grain refinement is visible. On the other hand, if the zirconium content is too high, coarse intermetallic phases are formed, which severely limit the ductility. On the other hand, if the titanium content is too low, no grain refinement is possible in die casting. The above-described excess of titanium in the ratio of titanium to zirconium accordingly results in improved strength in the cast state with sufficient ductility and joinability.

In a further advantageous development of the die-cast aluminum alloy, it can contain 0.2 to 0.5% by weight, in particular 0.32 to 0.4% by weight, of magnesium.

Alternatively or additionally, the aluminum die-cast alloy according to the invention can have 0.001 to 0.2% by weight, in particular 0.001 to 0.12% by weight, of copper.

The use of magnesium and/or copper results in an optional hardenability of the die-cast aluminum alloy according to the invention. The ratio of copper to magnesium is preferably kept below 0.66, resulting in improved protection against corrosion. By adding copper, the hardening of the aluminum die-cast alloy according to the invention, if it contains, as stated above, 0.2 to 0.5% by weight, in particular 0.32 to 0.4% by weight, of magnesium, can be outsourcing in a drying step of a painting process can be greatly accelerated. In addition to the ratio of copper to magnesium specified above, the limit of max. 0.2%, in particular max. 0.12%, of copper should not be exceeded, since otherwise increased corrosion of the component can occur. Furthermore, the die-cast aluminum alloy can have 0.05 to 0.4% by weight, in particular 0.12 to 0.25% by weight, of zinc. Zinc leads to a finer formation of the magnesium precipitates and thus improves the achievable strength in the T5 condition through the drying step of the painting process, while at the same time increasing the resistance to hot cracking.

Claim 2 specifies a method for the heat treatment of a component for a motor vehicle made from a hardenable die-cast aluminum alloy. The component is pre-stored for a period of 0.5 to 2 h, in particular 0.5 to 1 h, at a temperature of 120 to 190 °C, in particular 150 °C to 170 °C, and then for a period of 0 5 to 2 h at a temperature of 150 to 210 ° C subjected to a drying step of a painting process. With such a method, a component can be produced from a hardenable die-cast aluminum alloy with high strength and high ductility, with the components exhibiting very little distortion.

Surprisingly, it has been shown that a short pre-storage immediately after the casting can enormously accelerate the curing in the later painting process, ie in the drying step of the painting process. The heat treatment station required for this is also very small and can optionally be integrated into the casting cell. This results in the following advantages: There is no need for subsequent heat treatment of the component, and there are no furnace systems for this. Instead, the full curing potential can be achieved in the painting process thanks to a short pre-storage period. Due to the accelerated curing, very high strengths can be generated even in the painting process with low temperatures and short times, which means that very thin-walled components with low weight are possible. The strength increases only slightly during pre-aging, which means that joining operations can continue to benefit from the low strength. The actual curing is then accelerated in the drying step of the painting process. The corrosion properties remain very good, thanks to the accelerated hardening the use of high proportions of copper can be dispensed with due to the pre-storage.

A particularly high ratio of strength and ductility can be achieved by combining pre-ageing with an optimized alloy composition.

Another method for the heat treatment of an aluminum die-cast alloy according to claim 1, wherein 0.2 to 0.5% by weight, in particular 0.32 to 0.4% by weight, magnesium and 0.001 to 0.2% by weight -%, in particular 0.001 to 0.12% by weight, copper are provided in the aluminum die-cast alloy, produced component for a motor vehicle results from claim 3. The aluminum die-cast alloy has 0.2 to 0.5 wt. %, in particular 0.32 to 0.4% by weight, magnesium and/or 0.001 to 0.2% by weight, in particular 0.001 to 0.12% by weight, copper and the component is for a period of 0.5 to 2 h at a temperature of 150 to 210 ° C subjected to a drying step of a painting process. Such a T5 heat treatment, which is part of the drying step of a painting process, results in maximum hardening, which results in high strength and a high lightweight construction potential for the component.

A component for a motor vehicle, in particular a large-volume and/or large-area structural component for a body of the motor vehicle, produced from an aluminum die-cast alloy according to claim 1 or produced according to a method according to claim 2 or 3, is specified in claim 4.

The following table shows different die-cast aluminum alloys as well as certain features and physical sizes determined by tests and, if applicable, their characteristics. The alloys marked "SdT" are known from the general state of the art, the alloys marked "Erf" correspond to the requirements of patent claim 1 and possibly one or more dependent claims. The information in the "Corrosion" column describes poor, average, good or very good corrosion properties of the respective alloy:

* ¹ Tactile measurement of real cast components when installed in the vehicle

(Mean value of all deviations in terms of amount)

* ² DIN EN ISO 9227NSS * ³ Hot crack length through a MIG metal inert gas weld seam at the weld seam end crater

It can be seen from the table that the alloys marked “Erf”, which meet the requirements of patent claim 1 and possibly one or more subclaims, are not better in all features or properties than those marked “SdT”. general prior art known alloys, but that none of their features or properties of use as a component for a motor vehicle, in particular as large-volume and / or large-area structural component for a body of a motor vehicle.

The alloy AISi7MnO.4MgO.3NiO.2ZnO.2CuO.1 (T5 by means of pre-aging and subsequent painting process) meets the requirements to a particularly high degree and, despite good joinability after pre-aging, achieves the strength level of the T6 alloy through the drying step within the painting process.

Further properties of the aluminum die-casting alloy according to the invention are explained below with the aid of several diagrams.

It shows:

1 shows a diagram in which a change in the yield point R _P o.2 and the elongation at break A is shown as a function of the nickel content in the aluminum die-casting alloy;

2 shows a diagram in which the flowability is shown as a function of the nickel content; and

3 shows a diagram in which the yield point R _P o.2 and the elongation at break A are shown as a function of the titanium and zirconium content in the aluminum die-casting alloy.

4 shows a diagram in which the yield strength R _P o.2 is shown as a function of the duration of the drying step of a painting process and prior storage.

From Fig. 1, in which a change in the yield point R _P o.2 and the elongation at break A is shown as a function of the nickel content in the aluminum die-cast alloy, it can be seen that the use of nickel in an aluminum die-cast alloy, as long as a Share of 0.3 wt .-%, in particular 0.2 wt .-%, is not exceeded, the strength in Cast condition is increased without affecting ductility. However, the ductility drops very sharply at higher levels. In addition, nickel also acts against mold sticking, which means that the proportion of manganese can be reduced, which in turn improves ductility. The yield strength R _P o.2 and the elongation at break A of an AISi7 base alloy are shown with "Reference". The area marked “1” shows the area in which the alloy has an optimal balance of strength and ductility.

In FIG. 2, in which the flowability is shown as a function of the nickel content, it can be seen that the flowability of the alloy also reaches an optimum in the area marked “1”.

FIG. 3 shows a diagram in which the yield point R _P o.2 and the elongation at break A are shown as a function of the titanium and zirconium content for four different aluminum die-cast alloys. In this case, “2” designates an alloy in which the titanium content is too low and therefore no effect can be achieved. The alloy designated "3" has the best combination of strength and ductility and only fine phases could be observed in the structure. The zirconium content of the alloy marked “4” was too high, causing the ductility to drop. The structure showed very coarse phases.

The diagram shows that, in contrast to known solutions, in which titanium contents of 0.05 to 0.10% by weight and higher zirconium contents of 0.15 to 0.30% by weight are used a proportion of 0.18% by weight titanium and 0.06% by weight zirconium is particularly effective, since here both strength and ductility increase and grain refinement is visible. On the other hand, if the zirconium content is too high, coarse intermetallic phases are formed, which severely limit the ductility. On the other hand, if the titanium content is too low, no grain refinement is possible in die casting. The ratio and the amount of the alloy components titanium and zirconium therefore have an impact on the physical properties of the aluminum die-cast alloy. From the diagram of Fig. 4, in which the course of the yield point over the duration of the drying step of a painting process, in particular a cathode dip painting (KTL), for the alloy AISi7MnO.4MgO.3NiO.2ZnO.2CuO.1 with and without pre-aging is shown, it can be seen that the curing of the component is significantly accelerated with pre-storage. In addition to cathode dip painting, anode dip painting or another suitable method is also conceivable within the painting process.

Claims

PATENT CLAIMS:

1. Die-cast aluminum alloy with the following alloy components:

5 to 9% by weight, in particular 6.5 to 8% by weight, silicon, 0.05 to 0.3% by weight, in particular 0.1 to 0.2% by weight, nickel, manganese, the proportion of this element being 0.2 to 0.6% by weight, optionally 0.008 to 0.025% by weight, in particular 0.01 to 0.02% by weight, strontium, optionally 0.05 to 0. 2 wt%, especially 0.11 to 0.18 wt% titanium, optionally 0.05 to 0.15 wt%, especially 0.05 to 0.10 wt% zirconium, optional 0.2 to 0.5 wt%, especially 0.32 to 0.4 wt% magnesium, optionally 0.001 to 0.2 wt%, especially 0.001 to 0.12 wt% copper , optionally 0.05 to 0.4% by weight, in particular 0.12 to 0.25% by weight, zinc, remainder aluminum and unavoidable impurities.

2. Process for the heat treatment of a component for a motor vehicle made from a hardenable die-cast aluminum alloy, the component being heated for a period of 0.5 to 2 h, in particular 0.5 to 1 h, at a temperature of 120 to 190 °C, in particular 150 °C to 170 °C, and then subjected to a drying step of a painting process for a period of 0.5 to 2 h at a temperature of 150 to 210 °C.

3. A method for the heat treatment of a component for a motor vehicle made from an aluminum die-cast alloy according to claim 1, wherein the component is subjected to a drying step of a painting process for a period of 0.5 to 2 hours at a temperature of 150 to 210 °C, wherein 0.2 to 0.5% by weight, in particular 0.32 to 0.4% by weight, magnesium and 0.001 to 0.2% by weight, in particular 0.001 to 0.12% by weight, copper in the die-cast aluminum alloy are provided. Component for a motor vehicle, in particular a large-volume and/or large-area structural component for a body of the motor vehicle, produced from an aluminum die-cast alloy according to Claim 1 or produced using a method according to Claim 2 or 3.