EP4093894B1

EP4093894B1 - Die cast aluminum alloys for structural components

Info

Publication number: EP4093894B1
Application number: EP21704681.2A
Authority: EP
Inventors: Jason STUCKI; Grant PATTINSON; Quinlin HAMILL; Avinash PRABHU; Sivanesh Palanivel; Omar LOPEZ-GARRITY
Original assignee: Tesla Inc
Current assignee: Tesla Inc
Priority date: 2020-01-22
Filing date: 2021-01-20
Publication date: 2024-10-09
Anticipated expiration: 2041-01-20
Also published as: CN115003832A; EP4093894A1; US20230046008A1; WO2021150604A1; KR20220129568A; EP4461435A2; JP2023510881A

Description

BACKGROUND

Field

The present invention relates to alloy compositions comprising aluminum alloys. More specifically, the present invention relates to aluminum alloys with improved strength, ductility, and castability for high-performance applications including automobile parts. The present invention further relates to an automobile article comprising said alloy composition and to a process for preparing the alloy.

Description of the Related Art

Commercial cast aluminum alloys for certain applications, for example structural components within an electric vehicle chassis, generally require both high strength and ductility. It is desirable to form these parts through a casting process, such that the parts may be cast quickly and reliably, such as through a high pressure die casting process. After casting, suitable alloys should maintain their structural properties sufficiently for the necessary application. Poor castability of the alloy often results in observed hot tearing, and can cause fill issues which typically decreases the mechanical properties of the part that results from the casting process. Furthermore, many structural components that are die cast may require heat treating, quenching, solution treating or aging the component after being cast to improve strength or ductility. However, heat treatment may require a large capital expenditure, long process time, and can cause costly yield loss. These issues are compounded by large part sizes which may be complicated to put through a heat treatment process, such as a quenching process.
US 2017/107599 A1 describes copper-free aluminum alloys suitable for high pressure die casting and capable of age-hardening under elevated temperatures.
It may be desirable to produce cast aluminum alloys with high yield strengths such that the alloys do not fail easily, while also containing sufficient ductility. Furthermore, it may be desirable to produce cast aluminum alloys that do not require a heat treatment.

SUMMARY

The invention is set out in the appended set of claims. For purposes of summarizing the disclosure and the advantages achieved over the prior art, certain objects and advantages of the disclosure are described herein. Not all such objects or advantages may be achieved in any particular embodiment. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.
In one aspect of the invention, an alloy composition is disclosed as defined in claim 1. The alloy composition comprises Si at about 6-11 wt.%; Cu at about 0.3-0.8 wt.%; Mn at about 0.3-0.8 wt.%; Mg at about 0.1-0.4 wt.%; Fe at most about 0.5 wt.%; V at about 0.05-0.15 wt.%; Sr at about 0.01-0.05 wt.%; Ti at most about 0.15 wt.%; Cr at most about 0.03 wt.%; and remainder Al and incidental impurities, wherein the incidental impurities are at most about 0.1 wt.%, wherein the alloy comprises a yield strength of at least about 130 MPa and a bend angle of at least about 20° at a 3 mm section thickness when as-cast and without further processing.
In some embodiments, the alloy comprises a bend angle of at least about 24° at a 3 mm section thickness when as-cast and without further processing. According to the invention, the alloy comprises an α-Al volume fraction of at least about 90%.
In some embodiments, the alloy comprises about 0.03 wt.% to about 0.25 wt.% of Mg₂Si phases. In some embodiments, the alloy comprises about 0.01 wt.% to about 0.9 wt.% of Al₂Cu phases. In some embodiments, the alloy comprises about 0.03 wt.% to about 0.2 wt.% of AlCuMgSi phases. In some embodiments, the alloy comprises about 0.3 wt.% to about 3 wt.% of AlFeSi phases. In some embodiments, the alloy composition further comprises Cu and Mg, wherein a weight ratio of Cu:Mg is about 4:1 to about 2:1.
In some embodiments, the alloy composition comprises:

Si at about 6.5-7.5 wt.%;
Cu at about 0.4-0.8 wt.%;
Mn at about 0.3-0.7 wt.%;
Mg at about 0.1-0.4 wt.%;
Fe at most about 0.4 wt.%;
V at about 0.05-0.15 wt.%;
Sr at about 0.01-0.03 wt.%;
Ti at most about 0.15 wt.%;
Cr at most about 0.03 wt.%; and
remainder Al and incidental impurities.

In some embodiments, the alloy composition comprises:

Si at about 6-11 wt.%;
Cu at about 0.3-0.8 wt.%;
Mn at about 0.3-0.8 wt.%;
Mg at about 0.15-0.4 wt.%;
Fe at most about 0.5 wt.%;
V at about 0.05-0.15 wt.%;
Sr at about 0.01-0.05 wt.%;
Ti at most about 0.15 wt.%;
Cr at most about 0.03 wt.%; and
remainder Al and incidental impurities.

According to the invention, the incidental impurities are at most about 0.1 wt.%.
In another aspect of the invention, an automobile article including the alloy composition is disclosed as defined in claim 10. In some embodiments, the automobile article is an automobile chassis.
In one aspect of the invention, a process for preparing an alloy is disclosed as defined in claim 11. The process includes providing alloy components as defined in the alloy composition disclosed herein, melting the alloy components to form a melted alloy, and cooling the melted alloy to form an as-cast alloy, wherein the as-cast alloy comprises a yield strength of at least about 130 MPa and a bend angle of at least about 20° at a 3 mm section thickness.
In some embodiments, further processing is not performed on the as-cast alloy. In some embodiments, the process further comprises die-casting the melted alloy. In some embodiments, die-casting is high-pressure die-casting (HPDC). In some embodiments, the process further comprises further processing the as-cast alloy to form a processed alloy. In some embodiments, the further processing step is selected from the group consisting of heat treating, aging, solution treating, surface finishing and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing bend angles and yield strengths numerous commercial alloys and the target alloys of some embodiments.
FIG. 2 is a bar chart showing the predicted and tested yield strengths of alloys of some embodiments.
FIG. 3A is a plot of bend angles and α-aluminum volume fractions for alloys of some embodiments.
FIG. 3B is a plot of bend angles and magnesium/nickel content for alloys of some embodiments.
FIG. 4 is a bar chart showing the predicted and tested normalized flow lengths of alloys of some embodiments.
FIG. 5 is a plot showing bend angles and yield strengths for alloys of some embodiments.
FIG. 6A is a bar chart showing experimental results of flow lengths and silicon content for alloys of some embodiments.
FIG. 6B is a line graph showing calculated results demonstrating the relationship between bend angle and FCC mole fraction as a function of silicon content for alloys of some embodiments.
FIG. 7 is a predictive model chart showing yield strengths at Cu:Mg ratios of 3:1 at various magnesium and silicon weight percentages for alloys of some embodiments.
FIG. 8A is a plot showing experimental results of bend angle for alloys of some embodiments including various magnesium and strontium amounts.
FIG. 8B is a plot showing experimental results of tensile yield strength and bend angles for alloys of some embodiments with varying copper and magnesium weight percentages.
FIG. 9A is an optical micrograph cross-sectional image of a comparative alloy.
FIG. 9B is an optical micrograph cross-sectional image of an alloy according to some embodiments.
FIG. 10A is an optical micrograph cross-sectional image of an aluminum and silicon alloy.
FIG. 10B is an optical micrograph cross-sectional image of an aluminum, silicon and strontium alloy.

DETAILED DESCRIPTION

The present disclosure may be understood by reference to the following detailed description. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale, may be represented schematically or conceptually, or otherwise may not correspond exactly to certain physical configurations of embodiments.
Embodiments relate to aluminum alloys useful for creating products such as vehicle chassis or chassis components. For example, the vehicle can be an electric vehicle powered by a battery pack. In one embodiment, the alloys were created to provide sufficient castability, and also provide relatively high yield strength and ductility, as well as eliminating the need for subsequent heat treatment of the cast alloy. According to the invention, the alloy comprises a yield strength of at least about 130 MPa and a bend angle of at least about 20° at a 3 mm section thickness when as-cast and without further processing. The aluminum alloys comprise vanadium to provide many of these enhancements. In another embodiment, the aluminum alloy has a specific weight ratio of copper to magnesium to provide many of these enhancements of an alloy with the desired features In one embodiment, the aluminum alloy has a weight ratio of Cu:Mg of about 4:1 to about 2:1. As mentioned below, aluminum alloys with these compositions were found to have high yield strength and high ductility compared to available aluminum alloys. As mentioned below, the aluminum alloys are described herein by the weight percent (wt %) of the total elements and particles within the alloy, as well as specific properties of the alloys. It will be understood that the remaining composition of any alloy described herein is aluminum and incidental impurities.

Aluminum Alloy Compositions

FIG. 1 is a chart showing bend angles and yield strengths numerous commercial high pressure die cast (HPDC) alloys. The target alloy mechanical requirements in FIG. 1 are shown to be greater than 135 MPa yield strength and greater than 24 degree bend angle. However, FIG. 1 demonstrates that the commercial alloys either require heat treatment to meet the necessary mechanical requirements, or do not meet the necessary requirements.
In contrast, embodiments of the disclosure relate to casting aluminum alloys with both high yield strength and high ductility, without the need for post-casting heat treatment. The aluminum alloys were found to have high yield strength and high ductility compared to conventional, commercially available aluminum alloys. The aluminum alloys are described herein by the weight percent (wt %) of the total elements and particles within the alloy, as well as specific properties of the alloys. It will be understood that the remaining composition of any alloy described herein is aluminum and incidental impurities.
Impurities may be present in the starting materials or introduced in one of the processing and/or manufacturing steps to create the aluminum alloy. Incidental impurities are compounds and/or elements that do not or do not substantially affect the material properties of the composition, such as yield strength, ductility and eliminating the need for heat treatment. According to the invention, the total incidental impurities are at most about 0.1 wt%. In some embodiments, each elemental incidental impurity is at most, or is at most about, 0.1 wt.%, 0.05 wt.%, 0.01 wt.%, 0.005 wt.% or 0.001 wt.%, or any range of values therebetween.
In some embodiments, the aluminum alloy composition comprises Si in the range of, or of about, 6.5-7.5 wt %, Cu in the range of, or of about, 0.4-0.8 wt %, Mn in the range of, or of about, 0.3-0.7 wt %, Mg in the range of, or of about, 0.2-0.4 wt %, Fe of at most, or of at most about, 0.4 wt %, V in the range of, or of about, 0.05-0.15 wt %, Sr in the range of, or of about, 0.01-0.03 wt %, Ti of at most, or of at most about, 0.15 wt %, Cr of at most, or of at most about, 0.03 wt %, with the remaining composition (by wt %) being Al and incidental impurities, wherein the maximum incidental impurities total 0.15 or 0.1 wt %. In some embodiments, each elemental incidental impurity is, is about, is at most, or is at most about 0.05 wt %.
In some embodiments, the aluminum alloy composition comprises Si in the range of, or of about, 6.5-11 wt %, Cu in the range of, or of about, 0.3-0.8 wt %, Mn in the range of, or of about, 0.3-0.8 wt %, Mg in the range of, or of about, 0.1-0.4 wt %, Fe of at most, or of at most about, 0.5 wt %, V in the range of, or of about, 0.05-0.15 wt %, Sr in the range of, or of about, 0.01-0.05 wt %, Ti of at most, or of at most about, 0.15 wt %, Cr of at most, or of at most about, 0.03 wt %, with the remaining composition (by wt %) being Al and incidental impurities, wherein the maximum incidental impurities total 0.1 wt %. In some embodiments, each elemental incidental impurity is, is about, is at most, or is at most about 0.05 wt %.
In some embodiments, the aluminum alloy composition comprises silicon (Si) in an amount of, of about, of at most, or of at most about, 11 wt.%, 10 wt.%, 9 wt.%, 8 wt.%, 7 wt.%, or 6 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises copper (Cu) in an amount of, of about, of at most, or of at most about, 0.8 wt.%, 0.7 wt.%, 0.6 wt.%, 0.5 wt.%, 0.4 wt.%, or 0.3 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises manganese (Mn) in an amount of, of about, of at most, or of at most about, 0.6 wt.%, 0.5 wt.%, 0.45 wt.%, 0.4 wt.%, 0.35 wt.%, or 0.3 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises iron (Fe) in an amount of, of about, of at most, or of at most about, 0.5 wt.%, 0.4 wt.%, 0.3 wt.%, 0.2 wt.%, 0.1 wt.%, 0.05 wt.%, or 0.01 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises vanadium (V) in an amount of, of about, of at most, or of at most about0.1 wt.% or 0.05 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises strontium (Sr) in an amount of, of about, of at most, or of at most about0.05 wt.%, 0.045 wt.%, 0.04 wt.%, 0.035 wt.%, 0.03 wt.%, 0.025 wt.%, 0.02 wt.%, 0.015 wt.%, or 0.01 wt.% or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises titanium (Ti) in an amount of, of about, of at most, or of at most about, 0.15 wt.%, 0.14 wt.%, 0.13 wt.%, 0.12 wt.%, 0.1 wt.%, 0.08 wt.%, 0.07 wt.%, 0.06 wt.%, 0.05 wt.%, 0.04 wt.%, 0.03 wt.%, 0.02 wt.%, 0.01 wt.% or 0.005 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises chromium (Cr) in an amount of, of about, of at most, or of at most about, 0.03 wt.%, 0.02 wt.%, 0.01 wt.% or 0.005 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises each elemental incidental impurity in an amount of, of about, of at most, or of at most about, 0.1 wt.%, 0.07 wt.%, 0.05 wt.%, 0.04 wt.%, 0.03 wt.%, 0.02 wt.%, 0.01 wt.% or 0.005 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises a maximum incidental impurities total in an amount of, of about, of at most, or of at most about, 0.1 wt.%, 0.07 wt.%, 0.05 wt.%, 0.04 wt.%, 0.03 wt.%, 0.02 wt.%, 0.01 wt.% or 0.005 wt.%, or any range of values therebetween.
In some embodiments, the aluminum alloy composition comprises a weight ratio of Cu:Mg in an amount of, or of about, 4:1, 3.5:1, 3:1, 2.5:1, or 2:1, any range of values therebetween.
In some embodiments, the α-Al volume fraction of an alloy is, is about, is at least, or is at least about, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, or any range of values therebetween.
In some embodiments, the aluminum alloy composition comprises Mg₂Si phases in, in about in less than, or less than about, 0.25 wt.%, 0.2 wt.%, 0.15 wt.%, 0.1 wt.%, 0.05 wt.%, 0.04 wt.%, or 0.03 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises Al₂Cu phases in, in about, in less than, or less than about, 0.9 wt.%, 0.8 wt.%, 0.7 wt.%, 0.6 wt.%, 0.5 wt.%, 0.45 wt.%, 0.4 wt.%, 0.35 wt.%, 0.3 wt.%, 0.25 wt.%, 0.2 wt.%, 0.15 wt.%, 0.1 wt.%, 0.05 wt.%, 0.04 wt.%, 0.03 wt.%, 0.02 wt.%, or 0.01 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises AlCuMgSi phases in, in about, in at least, or in at least about, 0.2 wt.%, 0.15 wt.%, 0.1 wt.%, 0.05 wt.%, 0.04 wt.%, or 0.03 wt.%, or any range of values therebetween. In some embodiments, the aluminum alloy composition comprises AlFeSi phases in, in about, in less than, less than about, in at least, or in at least about, 3 wt.%, 2.9 wt.%, 2.8 wt.%, 2.7 wt.%, 2.6 wt.%, 2.5 wt.%, 2.4 wt.%, 2.2 wt.%, 2 wt.%, 1.8 wt.%, 1.5 wt.%, 1.2 wt.%, 1 wt.%, 0.9 wt.%, 0.8 wt.%, 0.7 wt.%, 0.6 wt.%, 0.5 wt.%, 0.45 wt.%, 0.4 wt.%, 0.35 wt.%, or 0.3 wt.%, or any range of values therebetween.

Alloy Yield Strength

Industrial applications in which thousands and hundreds-of-thousands of aluminum alloy parts may be cast can require high yield strength. As seen in, FIG. 2 the predicted and tested yield strengths of alloys of embodiments 1B3, 2F5, 3D2, 3C1, 3I1, 365-3, 365-2, 1B4, 3C3a, 3C3b, 3I3a, 3I3b and 3D3 were evaluated.
The yield strength of the aluminum alloys described herein are at least or at least about 130 MPa. In some embodiments, the yield strength is, is about, is at least, or is at least about, 130 MPa, 135 MPa, 140 MPa, 145 MPa, 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, 180 MPa or 200 MPa, or any range of values therebetween. In some embodiments, the yield strength is, or is about, 130 MPa, 135 MPa, 140 MPa, 145 MPa, 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, 180 MPa or 200 MPa, or any range of values therebetween.

Alloy Ductility

The ductility of metal alloy should also be considered such that the parts are reproducibly manufacturable by using a casting process. Ductility of an alloy may be measured by the bend angle and/or the elongation of the alloy, although bend angle is preferred.
FIG. 3A is a plot of bend angles and α-aluminum volume fractions for alloys, and FIG. 3B is a plot of bend angles and magnesium/nickel content for alloys of some embodiments.
In some embodiments, bend angle of an alloy is, is about, is at least, or is at least about, 20°, 23°, 25°, 30°, 35°, 40°, or 50°, or any range of values therebetween. In some embodiments, bend angle is, or is about, 20°, 23°, 25°, 30°, 35°, 40°, 50° or 60°, or any range of values therebetween. In some embodiments, the bend angle is measured at a 3 mm section thickness. According to the invention, the bend angle is measured using the VDA238-100 evaluation standards.

Die Cast Performance and Flowability

In addition to sufficient yield strength and ductility when cast, the as-cast aluminum alloy must provide sufficient flowability and resistance to hot tearing and shrinkage cracking when high pressure die cast (HPDC). Unless specified otherwise, flow lengths described herein are under HPDC conditions. In a metal casting process, the metal alloy must have sufficient flowability to flow into and fill all intricacies of the mold. In molds with narrow and/or long mold channels, a sufficiently high flowability of the alloy is required to fill the mold. FIG. 4 is a bar chart showing the predicted and tested normalized flow lengths under HPDC conditions of alloys of some embodiments.
A formula for predicting the flow length of alloys within a sand casting under HPDC conditions is shown below. $L_{f} = \frac{ρ^{0.2}}{(T_{0.65} - T_{0})} (H_{L} + c_{p} Δ T)$
Hot tearing and shrinkage cracking are common and catastrophic defects observed when casting alloys, including aluminum alloys. Without being able to prevent hot tearing in alloy, reliable and reproducible parts cannot be created. Hot tearing is the formation of an irreversible crack while the cast part is still in the semisolid casting. Although hot tearing is often associated with the casting process itself-linked to the creation of thermal stresses during the shrinkage of the melt flow during solidification, the underlying thermodynamics and microstructure of the alloy plays a part.
In some embodiments, the alloy has a casting flow length under HPDC conditions of, of about, of at least, or of at least about, 1.8 m, 1.9 m, 2 m, 2.2 m, 2.5 m, 3 m or 5 m, or any range of values therebetween. In some embodiments, the alloy does not, or does not substantially, develop hot tears and/or shrinkage cracks throughout the casting flow length.

Corrosion/Oxidation Resistance

Structural castings are expected to last within punishing environments for automotive applications. In some embodiments, the as-cast alloys are resistant to corrosion and/or oxidation. The alloy can have an oxygen reduction factor (ORF) with respect to A380 kinetics of, of about, of at most, or of at most about, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2 or 0.1, or any range of values therebetween.

Processing Methods

In some embodiments, a melt for an alloy can be prepared by heating the alloy above the melting temperature of the alloy components. As the melt is cast and cooled to room temperature, the alloys may go through cooling at various rates. The processing conditions can create larger or smaller grain sizes, increase or decrease the size and number of precipitates, and help minimize as-cast segregation.
In some embodiments, the alloy is die-cast. In some embodiments, the alloy is high pressure die-cast (HPDC). In certain embodiments, the aluminum alloy is cast without further processing. In some embodiments, the as-cast aluminum alloy is not further processed through heat treatment, and maintains the yield strength and ductility as mentioned above. In other embodiments, the as-cast aluminum alloy is further processed. In some embodiments, further processing methods include heat treating, aging, solution treating and surface finishing.
In certain embodiments, the after the aluminum-alloy melt has been formed, it may be cast into a die to form a high-performance product or part. In some embodiments, product can be part of an automobile, such as parts of chassis and/or other crash components.

EXAMPLES

Example 1

Predictive models were performed to calculate yield strengths and ductility (e.g. bend angle) of aluminum alloy cast without further heat treatment processing. A number of predictive aluminum alloy compositions were created and experimentally tested for their as-cast yield strengths and ductility without heat treatment, including compositions 3C1, 3C3a, 3C3b, 3C4, 3C5, 3C6, 3C7, 3C8, 3C9 and 3C10. The results of these experimental tests are shown in FIG. 5, which is a plot showing bend angles and yield strengths of alloy compositions 3C1, 3C3a, 3C3b, 3C4, 3C5, 3C6, 3C7, 3C8, 3C9 and 3C10.

The elemental weight percent compositions of alloy compositions 3C1, 3C3a, 3C3b, 3C4, 3C5, 3C6, 3C7, 3C8, 3C9 and 3C10, with the remainder of the compositions being aluminum, are shown below in Table 1. The as-cast aluminum alloy composition of 3C10 was found to have a yield strength of about 143 MPa and a bend angle of about 25°, and the composition of aluminum alloy 3C10 that falls within

Alloys

1, 2 and 3 shown below in Table 2.

Table 1

Alloy ID	Composition (wt%)
Alloy ID	Al	Si	Mg	Mn	Ni	Cu	Fe	Ti	Sn	V	Sr
3C1	Remain	6	-	1	-	0.5	0.2	-	0.05	-	0.03
3C3a	Remain	7	-	0.45	-	0.8	0.2	-	-	-	0.03
3C3b	Remain	7	0.3	0.45	-	0.8	0.2	-	-	-	0.03
3C4	Remain	6.5	0.25	0.35	-	0.75	0.2	0.1	-	0.15	0.03
3C5	Remain	5	0.3	0.35	-	0.9	0.2	0.10	-	0.15	0.03
3C6	Remain	6.5	0.15	0.35	-	0.45	0.2	0.10	-	0.15	0.03
3C7	Remain	6.5	0.15	0.35	0.05	0.45	0.2	0.10	-	0.15	0.03
3C8	Remain	6.5	0.15	0.35	-	0.45	0.2	-	-	0.15	0.03
3C9	Remain	7	0.25	0.35	-	0.5	0.2	0.05	-	0.1	0.03
3C10	Remain	7	0.15	0.45	-	0.8	0.2	0.05	-	0.1	0.03

Table 2

Element	Alloy 1	Alloy 2	Alloy 3
Al	Remainder	Remainder	Remainder
Si	6.5-7.5 wt.%	6-11 wt.%	6-11 wt.%
Cu	0.4-0.8 wt.%	0.3-0.8 wt.%	0.3-0.8 wt.%
Mn	0.35-0.7 wt.%	0.35-0.8 wt.%	0.35-0.8 wt.%
Mg	0.1-0.4 wt.%	0.15-0.4 wt.%	0.1-0.4 wt.%
Fe	≤ 0.4 wt.%	≤ 0.5 wt.%	≤ 0.5 wt.%
V	0.05-0.15 wt.%	0.05-0.15 wt.%	0.05-0.15 wt.%
Sr	0.015-0.03 wt.%	0.015-0.05 wt.%	0.015-0.05 wt.%
Ti	≤ 0.15 wt.%	≤ 0.15 wt.%	≤ 0.15 wt.%
Cr	≤ 0.03 wt.%	≤ 0.03 wt.%	≤ 0.03 wt.%
Impurities	0-0.15 wt.%	0-0.15 wt.%	0-0.15 wt.%

Example 2

Although increased silicon content is known to decrease the ductility of an alloy, under traditional die casting conditions for aluminum alloys, silicon content is relatively high, at about 8-12 wt.% in order to have sufficient flowability when cast. This is because the relative increase of heat of fusion attributed to silicon content allows an increase in latent heat contribution such that heat may be retained within the alloy system when cast, and therefore the alloy may retain its liquid phase for enough time to achieve sufficient casting lengths. However, it is not readily apparent if the same silicon concentrations are necessary for flowability when the alloy is cast in HPDC condition.
FIG. 6A is a bar chart showing experimental results of flow lengths and silicon content for alloys of some embodiments under HPDC conditions through a 3 mm section thickness. Castings were made using an about 700 ton high pressure die casting machine and a die designed to maintain even flow front for a 3mm thick casting up to 2 m in length. The various alloys were tested with the same casting conditions and the castings flow length was quantified.
FIG. 6A shows that an alloy composition with 7.5 wt.% silicon had a flow length of about 1.4 meters, an alloy composition with 8.5 wt.% silicon had a flow length of about 1.45 meters, and an alloy composition with 9.5 wt.% silicon had a flow length of about 1.45 meters. As seen, there is a steep drop off in flowability gains of flow length for Si content over 7.5 wt%. Therefore, it was determined that silicon ranges for the alloy composition should be maintained over 6 wt.% to achieve advantageous flow lengths, but could be less than 11 wt.% (e.g. 8 wt.% or 7.5 wt.%) to minimize eutectic silicon phase's effect on reducing ductility. As such, under HPDC conditions it was discovered that increasing silicon content, relative to silicon content under traditional die casting conditions, did not necessarily improve flow length grow to as great of a degree. This discovery allowed the alloy silicon content to be reduced in order to achieve a HPDC case alloy with relatively longer flow lengths and an improved ductility.
FIG. 6B is a line graph showing calculated results demonstrating the relationship between bend angle and FCC (i.e. aluminum matrix) mole fraction as a function of silicon content for alloys of some embodiments. Whereas FCC of aluminum is the most ductile phase present in the alloy composition, the silicon eutectic phase is a relatively more brittle phase. FIG. 6B demonstrates such a relationship between aluminum and silicon, where increasing silicon content of the alloy results in a reduction in the FCC mole fraction and bend angle.

Example 3

FIG. 7 is a predictive model chart showing yield strengths at Cu:Mg ratios of 3:1 at various magnesium and silicon weight percentages for alloys of some embodiments. Although increases in copper, magnesium and/or silicon are calculated to increase yield strengths of the alloy in part through the formation of strengthening precipitates (e.g. Mg₂Si, Al₂Cu and AlCuMgSi), decreased aluminum content typically leads to a decrease in alloy ductility. However, FIG. 7 demonstrates that alloys within the silicon compositional ranges of Alloys 1, 2 or 3 of Table 2 and a Cu:Mg ratio of about 3:1 (e.g. 2:1 to 4:1) carefully balances yield strength and ductility. Such a Cu:Mg ratio selection unexpectedly and advantageously promotes the formation of the AlCuMgSi precipitate, which improves the alloys yield strength without substantially hindering ductility relative to other precipitates (e.g. Mg₂Si and/or Al₂Cu).
FIG. 8A is a plot showing experimental results of bend angles for alloys of some embodiments including various magnesium and strontium amounts. As demonstrated, magnesium solute content and Mg₂Si are both contributors to yield strength, but have negative effects on ductility.
FIG. 8B is a plot showing experimental results of tensile yield strength and bend angles for alloys of some embodiments with varying copper and magnesium weight percentages. As demonstrated, cast 3 mm coupon results matched predictions shown in FIG. 7 of improved yield strengths decreased ductility associated with increased magnesium content.

Example 4

FIGS. 9A and 9B are optical micrograph cross-sectional images of a comparative alloy and an alloy of the present disclosure, respectively, wherein indicated phases were located and analyzed using energy-dispersive X-ray spectroscopy (EDS). The comparative alloy of FIG. 9A includes less than 0.05 wt.% vanadium, which is outside of the range of Alloys 1, 2 and 3 of Table 2. In FIG. 9A, feature 902 is a AlFeSi(Mn) phase shown with a plate morphology that was found to include less than 0.2 wt.% V, and feature 904 is a AlFeSi(Mn + V) phase with globular morphology more favorable for ductility that was found to include greater than 1.2 wt.% V. A person of ordinary skill in the art would appreciate that increased sharp morphological features (e.g. plate morphologies) in part caused by iron impurities increase alloy crack initiation and propagation.
In contrast, the alloy of FIG. 9B shows a decrease in plate morphologies, and generally shows feature 906 of AlFeSi(Mn + V) phase with globular morphology more favorable for ductility, which was found to include greater than 1.2 wt.% V. As such, it is demonstrated that vanadium and manganese may be used to reduce iron impurity solubility and stabilize AlFeSi(Mn,V) phases that have a rounded morphology. This allows the alloy to maintain high ductility performance with higher tolerances of Fe.

Example 5

FIG. 10A is an optical micrograph cross-sectional image of an aluminum and silicon alloy with 9.5 wt.% silicon and remainder of aluminum and incidental impurities, and FIG. 10B is an optical micrograph cross-sectional image of an aluminum, silicon and strontium alloy with 9.5 wt.% silicon, added strontium and remainder of aluminum and incidental impurities. While FIG. 10A shows silicon eutectic phases with sharp morphologies known to reduce ductility, the use of a strontium alloy the modifier in FIG. 10B is shown to blunt the silicon phase growth and create an alloy with more rounded morphologies favorable for ductility.

Claims

An alloy composition, comprising:
Si at about 6-11 wt.%;

Cu at about 0.3-0.8 wt.%;

Mn at about 0.3-0.8 wt.%;

Mg at about 0.1-0.4 wt.%;

Fe at most about 0.5 wt.%;

V at about 0.05-0.15 wt.%;

Sr at about 0.01-0.05 wt.%;

Ti at most about 0.15 wt.%;

Cr at most about 0.03 wt.%; and

remainder Al and incidental impurities, wherein the incidental impurities are at most about 0.1 wt.%;

wherein the alloy comprises a yield strength of at least about 130 MPa and a bend angle of at least about 20° at a 3 mm section thickness when as-cast and without further processing, wherein the bend angle is measured using the VDA238-100 evaluation standards, and

wherein the alloy comprises an α-Al volume fraction of at least about 90%.
The composition of Claim 1, wherein the alloy comprises a bend angle of at least about 24° at a 3 mm section thickness when as-cast and without further processing.
The composition of any one of Claims 1 to 2, wherein the alloy comprises about 0.03 wt.% to about 0.25 wt.% of Mg₂Si phases.
The composition of any one of Claims 1 to 3, wherein the alloy comprises about 0.01 wt.% to about 0.9 wt.% of Al₂Cu phases.
The composition of any one of Claims 1 to 4, wherein the alloy comprises about 0.03 wt.% to about 0.2 wt.% of AlCuMgSi phases.
The composition of any one of Claims 1 to 5, wherein the alloy comprises about 0.3 wt.% to about 3 wt.% of AlFeSi phases.
The composition of any one of Claims 1 to 6, further comprising Cu and Mg, wherein a weight ratio of Cu:Mg is about 4:1 to about 2:1.
The composition of any one of Claims 1 to 3, comprising:
Si at about 6.5-7.5 wt.%;

Cu at about 0.4-0.8 wt.%;

Mn at about 0.3-0.7 wt.%;

Mg at about 0.1-0.4 wt.%;

Fe at most about 0.4 wt.%;

V at about 0.05-0.15 wt.%;

Sr at about 0.01-0.03 wt.%;

Ti at most about 0.15 wt.%;

Cr at most about 0.03 wt.%; and

remainder Al and incidental impurities, wherein the incidental impurities are at most about 0.1 wt.%; or

Si at about 6-11 wt.%;

Cu at about 0.3-0.8 wt.%;

Mn at about 0.3-0.8 wt.%;

Mg at about 0.15-0.4 wt.%;

Fe at most about 0.5 wt.%;

V at about 0.05-0.15 wt.%;

Sr at about 0.01-0.05 wt.%;

Ti at most about 0.15 wt.%;

Cr at most about 0.03 wt.%; and

remainder Al and incidental impurities, wherein the incidental impurities are at most about 0.1 wt.%.
An automobile article comprising the composition of any one of Claims 1 to 8, wherein the automobile article is preferably an automobile chassis.
A process for preparing an alloy, comprising:
providing the alloy components as defined in the alloy composition of any one of claims 1 to 8;

melting the alloy components to form a melted alloy; and

cooling the melted alloy to form an as-cast alloy;

wherein the as-cast alloy comprises a yield strength of at least about 130 MPa and a bend angle of at least about 20° at a 3 mm section thickness, wherein the bend angle is measured using the VDA238-100 evaluation standards.
The process of Claim 10, wherein further processing is not performed on the as-cast alloy.
The process of Claim 10, further comprising die-casting the melted alloy, wherein die-casting is preferably high-pressure die-casting.
The process of any one of Claims 10 or 12, further comprising further processing the as-cast alloy to form a processed alloy, wherein the further processing step is preferably selected from the group consisting of heat treating, aging, solution treating, surface finishing and combinations thereof.