US20210079501A1

US20210079501A1 - Low cost high ductility cast aluminum alloy

Info

Publication number: US20210079501A1
Application number: US17/079,818
Authority: US
Inventors: Juergen Wuest; Xiaoping Niu; Randy Beals
Original assignee: Magna International Inc
Current assignee: Magna International Inc
Priority date: 2015-03-17
Filing date: 2020-10-26
Publication date: 2021-03-18

Abstract

An aluminum alloy for casting into a component, such as a vehicle component, is provided. The aluminum alloy includes 2 to 5 wt. % silicon, which is a lower amount of silicon compared to other aluminum alloys used for casting. The aluminum alloy further includes 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy. The aluminum alloy can further include 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy. After the casting step, the cast aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.

Description

CROSS REFERENCE TO RELATED APPLICATION

This CIP Patent Application claims the benefit of U.S. patent application Ser. No. 15/061,257 filed on Mar. 4, 2016, entitled “Low Cost High Ductility Cast Aluminum Alloy,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/134,072, filed on Mar. 17, 2015, and entitled “Low Cost High Ductility Cast Aluminum Alloy,” the entire disclosures of the applications being considered part of the disclosure of this application and hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to an aluminum alloy for casting, a method of forming the aluminum alloy, a vehicle component formed of the cast aluminum alloy, and a method of manufacturing the cast component.

2. Related Art

Casting of aluminum alloys is oftentimes used in the automotive industry to form lightweight components, including complex structural, body-in-white, suspension, and chassis components. There are many types of known casting processes, for example high pressure die casting, low pressure casting, and squeeze casting. The die is typically formed of a hardened tool steel. Although the casting equipment is expensive, the cost per component formed is relatively low, which makes the process suitable for high volume production.
However, improvements to the casting process and materials used in the casting process are desired. For example, an aluminum alloy capable of forming a component having higher ductility, without loss of fluidity or castability, is desired. The aluminum alloy should also be resistant to damage associated with hot cracking, soldering, shrinkage, and corrosion. In addition, although lightweight components are desired, the components should still provide a high strength and toughness.

SUMMARY OF THE INVENTION

One aspect of the invention provides an aluminum alloy, comprising at least 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy.
Another aspect of the invention provides a method of manufacturing a component. The method comprises casting an aluminum alloy, the aluminum alloy including at least 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy.
A method of manufacturing an aluminum alloy, comprising the steps of: melting a 300 series aluminum alloy; and adding silicon to the melted 300 series aluminum alloy to form an improved aluminum alloy and so that the total amount of silicon present in the improved aluminum alloy is 2 to 5 wt. %, based on the total weight of the improved aluminum alloy. The improved aluminum alloy further includes at least 80 weight percent (wt. %) aluminum, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the improved aluminum alloy.
The cast aluminum alloy is able to achieve a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a graph illustrating the effect of silicon content on fluidity of an aluminum-silicon binary alloy;

FIG. 2 illustrates a portion of an example component formed of an aluminum alloy according to an embodiment of the invention;

FIG. 3 is a photomicrograph of the component of FIG. 2;

FIG. 4 illustrates method steps used to form the component of FIG. 2 according to an example embodiment;

FIG. 5 includes the composition of the aluminum alloy according to an example embodiment of the invention and mechanical properties of cast samples having a 3 mm thickness and formed of that example aluminum alloy.

DESCRIPTION OF THE ENABLING EMBODIMENT

One aspect of the invention provides an improved aluminum alloy for casting components, such as a lightweight automotive vehicle component, is provided. Examples of such components include structural, body-in-white, suspension, or chassis components. The aluminum alloy provides a component with improved ductility and elongation, and without hot tearing or loss of fluidity or castability. The aluminum alloy is also less expensive than other aluminum alloys used for casting, which is especially beneficial for high volume production.
The improved aluminum alloy is aluminum-based, and thus typically includes aluminum in an amount of at least 80 weight percent (wt. %), based on the total weight of the aluminum alloy. In one embodiment, the aluminum alloy is formed by modifying a 300 series aluminum alloy. A specific example of the 300 series aluminum alloy is an A356.2 aluminum alloy obtained from recycled road wheels. The A356.2 aluminum alloy includes 91.3 to 93.2 wt. % aluminum, not greater than 0.10 wt. % copper, not greater than 0.12 wt. % iron, 0.30 to 0.45 wt. % magnesium, not greater than 0.05 wt. % manganese, 6.5 to 7.5 wt. % silicon, not greater than 0.20 wt. % titanium, not greater than 0.05 wt. % zinc, other elements each in an amount of not greater than 0.05 wt. %, and other elements in a total amount of not greater than 0.15 wt. %, based on the total weight of the improved aluminum alloy. However, other types of aluminum alloys could be modified to form the improved aluminum alloy.
The aluminum alloy also includes an amount of silicon (Si) which helps achieve the improved elongation and ductility with reduced costs. The amount of silicon ranges from 2 to 5 wt. %, based on the total weight of the aluminum alloy. This amount of silicon is reduced compared to other aluminum alloys used for casting, which typically include 7.0 wt. % to 11.0 wt. % silicon. The lower amount of silicon present in the improved aluminum alloy creates a smaller eutectic phase, which leads to increased elongation in the finished component, as the eutectic phase is one of the main limitations for elongation. The elongation of a component formed of the improved aluminum alloy with reduced silicon content is typically 10% to 20%.
The reduced amount of silicon also reduces the total cost of the aluminum alloy. The castability, strength, and toughness of the aluminum alloy can also be adjusted based on the amount of silicon. In addition, it has been found that the reduced amount of silicon does not sacrifice fluidity or castability of the aluminum alloy, when compared to the other aluminum alloys which include 7.0 wt. % silicon or greater. In some cases, the castability of the improved aluminum alloy is better than that of the other aluminum alloys including 7.0 wt. % silicon or greater. Hot tearing is also avoided due to a lower amount of silicon. FIG. 1 is a graph illustrating the effect of silicon content on fluidity of an aluminum-silicon binary alloy.
Additional alloying elements can also be present in the improved aluminum alloy to further improve elongation and ductility, or to achieve the desired strength and toughness. For example, magnesium (Mg), manganese (Mn), and/or iron (Fe) can be added to further improve ductility, castability, strength, ductility, and/or toughness. In particular, the manganese can be used to prevent die sticking, and the magnesium can be used to form Mg₂Si for strengthening. The aluminum alloy can also include at least one of copper (Cu) and zinc (Zn) to increase strength, preferably without negatively impacting corrosion resistance. The zinc is also used as a solid solution strengthener and to improve machinability. The additional alloying elements can provide other metallurgical effects as well, such as improved resistance to hot cracking, soldering, shrinkage, and corrosion. For example, special properties or other metallurgical effects can be achieved by titanium (Ti). Strontium (Sr) can also be added to modify properties that occur due to the silicon. FIG. 2 illustrates a portion of an example component 10 formed of the improved aluminum alloy, and FIG. 3 is a photomicrograph 12 of a portion of the component 10 shown in FIG. 2.
According to one example embodiment, in addition to at least 80 wt. % aluminum and 2 to 5 wt. % silicon, the example aluminum alloy further includes 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy. The example embodiment can further include 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy. Typically, the aluminum alloy includes at least 0.16 wt. % iron, at least 0.3 wt. % manganese, at least 0.05 wt. % titanium, and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy. The total amount of manganese and iron together is preferably 0.6 to 0.8 wt. %, based on the total weight of the aluminum alloy. The manganese and iron can form an intermetallic phase that prevents the alloy from attacking tool steel of a die, which is typically caused by iron. When the aluminum alloy is cast, the cast aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.
According to another example embodiment, the aluminum alloy consists of, or consists essentially of, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, not greater than 0.6 wt. % manganese, and a reminder of aluminum in addition to possible impurities. The impurities, if present, are in an amount not greater than 0.15 wt. %. This example aluminum alloy could further consist of, or consist essentially of, the above elements plus 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy. The aluminum alloy could also consist of, or consist essentially of, the above elements plus at least 0.16 wt. % iron, at least 0.3 wt. % manganese, at least 0.05 wt. % titanium, and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy. FIG. 5 includes a specific example aluminum alloy according to an embodiment of the invention. This aluminum alloy consists or consists essentially of 4.17 wt. % silicon, 0.22 wt. % iron, 0.49 wt. % manganese, 0.4 wt. % magnesium, 1.35 wt. % zinc, 0.016 wt. % copper, 0.18 wt. % titanium, 0.06 wt. % strontium, and a reminder of aluminum in addition to possible impurities. The impurities, if present, are in an amount of not greater than 0.15 wt. %, based on the total weight of the aluminum alloy. A test was conducted to determine the yield strength (YS), ultimate tensile strength (UTS), and elongation (%) of eight sample castings formed of the aluminum alloy. The castings each had a thickness of 3 mm. For the eight samples, the average yield strength (YS) was 116.43 MPa, the average ultimate tensile strength (UTS) was 231.48 MPa, and the average elongation (%) was 12.20%.
Another aspect of the invention provides a method of manufacturing the aluminum alloy. FIG. 4 illustrates steps of the method according to an example embodiment. In one embodiment, the aluminum alloy is formed by modifying a 300 series aluminum alloy. The aluminum alloy is preferable obtained from recycled wrought aluminum. A specific example of the 300 series aluminum alloy is an A356.2 aluminum alloy obtained from recycled road wheels. The A356.2 aluminum alloy includes 91.3 to 93.2 wt. % aluminum, not greater than 0.10 wt. % copper, not greater than 0.12 wt. % iron, 0.30 to 0.45 wt. % magnesium, not greater than 0.05 wt. % manganese, 6.5 to 7.5 wt. % silicon, not greater than 0.20 wt. % titanium, not greater than 0.05 wt. % zinc, other elements each in an amount of not greater than 0.05 wt. %, and other elements in a total amount of not greater than 0.15 wt. %, based on the total weight of the improved aluminum alloy. However, other aluminum-based materials that could be used to form the improved aluminum alloy are sold by Cosma International or Magna International, such as Aural-4. Manufacturing the improved aluminum alloy from one of the recycled materials lowers the raw material cost, as it takes less energy to recycle an aluminum alloy than to create it from primary elements.
The method of forming the cast component typically begins by melting the recycled wrought aluminum, or other base aluminum alloy. The melting step can be conducted by an induction melter, or another source of heat. Once the base aluminum alloy is melted, the method includes adding silicon to the melt and mixing the silicon with the base aluminum alloy so that the total amount of silicon ranges from 2 to 5 wt. %, based on the total weight of the melted aluminum alloy, i.e. the final alloy composition. The additional alloying elements, discussed above, can be added to the melted mixture to form the improved aluminum alloy. Alternatively, the additional alloying elements could be present in the wrought aluminum or other base aluminum alloy. Once all of the elements are mixed together, the aluminum alloy is ready for casting.
The method then includes casting the aluminum alloy which includes at least 80 wt. % aluminum and 2 to 5 wt. % silicon, based on the total weight of the aluminum alloy. As discussed above, according to one example embodiment, in addition to at least 80 wt. % aluminum and 2 to 5 wt. % silicon, the example aluminum alloy further includes 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy. The example aluminum alloy can further include 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy. Typically, the aluminum alloy includes at least 0.16 wt. % iron, at least 0.3 wt. % manganese, at least 0.05 wt. % titanium, and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy. The total amount of manganese and iron is preferably 0.6 to 0.8 wt. %, based on the total weight of the aluminum alloy. After the casting step, the cast aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.
The cast component formed from the casting step can be, for example, a component for use in a vehicle. Any casting process used to form components from an aluminum-based material can be used with the improved aluminum alloy, for example high pressure die casting, low pressure casting, or squeeze casting. In one example embodiment, the casting process is a die casting process, which typically includes forcing the molten aluminum alloy into an unheated die or mold cavity under pressure. The die is typically formed from hardened tool steel. As discussed above, the castability and fluidity of the molten aluminum alloy with the reduced amount of silicon is equal to or slightly better than other aluminum alloys with higher amounts of silicon. The molten aluminum is formed to a solid component having the shape of the mold, which can be a complex shape. Many different types of components can be formed by the casting process, for example, a structural, body-in-white, suspension, or chassis component. After the casting process, the method can include an optional heat treating process or other finishing processes. However, it has been found that a heat treatment process may not be necessary when the component is formed from the improved aluminum alloy, which would provide the advantage of reduced process time and costs.
The component formed from the improved aluminum alloy has improved ductility and elongation due to the lower amount of silicon in the aluminum alloy. In addition, the aluminum alloy can include additional alloying elements to improve resistance to hot cracking, soldering, shrinkage, and corrosion, and also to achieve a desired strength and toughness, or even higher ductility. As discussed above, the cast component formed of the aluminum alloy typically has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the following claims.

Claims

What is claimed is:

1. An aluminum alloy, comprising:

at least 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy.

2. The aluminum alloy of claim 1 including 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy.

3. The aluminum alloy of claim 1, wherein the total amount of manganese and iron is 0.6 to 0.8 wt. %, based on the total weight of the aluminum alloy.

4. The aluminum alloy of claim 1, wherein the alloy is cast and has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20%.

5. The aluminum alloy of claim 1 including at least 0.16 wt. % iron and at least 0.3 wt. % manganese, based on the total weight of the aluminum alloy.

6. The aluminum alloy of claim 2 including at least 0.05 wt. % titanium and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy.

7. The aluminum alloy of claim 1, wherein the aluminum alloy is cast and formed into a component for a vehicle.

8. A method of manufacturing a component, comprising the steps of:

casting an aluminum alloy, the aluminum alloy including at least 80 weight percent (wt. %) aluminum, 2 to 5 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the aluminum alloy.

9. The method of claim 8, wherein the aluminum alloy includes 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the aluminum alloy.

10. The method of claim 8, wherein the aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20% after the casting step.

11. The method of claim 8, wherein the aluminum alloy includes at least 0.16 wt. % iron and at least 0.3 wt. % manganese, based on the total weight of the aluminum alloy.

12. The method of claim 9, wherein the aluminum alloy includes at least 0.05 wt. % titanium and at least 0.006 wt. % copper, based on the total weight of the aluminum alloy.

13. A method of manufacturing an aluminum alloy, comprising the steps of:

melting a 300 series aluminum alloy; and

adding silicon to the melted 300 series aluminum alloy to form an improved aluminum alloy and so that the total amount of silicon present in the improved aluminum alloy is 2 to 5 wt. %, based on the total weight of the improved aluminum alloy, and the improved aluminum alloy further includes at least 80 weight percent (wt. %) aluminum, 1.0 to 2.0 wt. % zinc, less than 0.5 wt. % iron, and not greater than 0.6 wt. % manganese, based on the total weight of the improved aluminum alloy.

14. The method of claim 13, wherein the improved aluminum alloy includes 0.01 to 0.07 wt. % strontium, 0.05 to 0.6 wt. % magnesium, not greater than 0.2 wt. % titanium, and less than 0.02 wt. % copper, based on the total weight of the improved aluminum alloy.

15. The method of claim 13, wherein the improved aluminum alloy includes a total amount of manganese and iron of 0.6 to 0.8 wt. %, based on the total weight of the improved aluminum alloy.

16. The method of claim 13 including casting the improved aluminum alloy, wherein the improved aluminum alloy has a yield strength of at least 110 MPa, ultimate tensile strength (UTS) of 220 to 230 MPa, and an elongation of 10 to 20% after the casting step.

17. The method of claim 16, wherein the casting step includes forming the aluminum alloy into a component for a vehicle.

18. The method of claim 13, wherein the improved aluminum alloy includes at least 0.16 wt. % iron and at least 0.3 wt. % manganese, at least 0.05 wt. % titanium, and at least 0.006 wt. % copper, based on the total weight of the improved aluminum alloy.

19. The method of claim 13, wherein the 300 series aluminum alloy includes 91.3-93.2 wt. % aluminum, not greater than 0.10 wt. % copper, not greater than 0.12 wt. % iron, 0.30 to 0.45 wt. % magnesium, not greater than 0.05 wt. % manganese, 6.5 to 7.5 wt. % silicon, not greater than 0.20 wt. % titanium, not greater than 0.05 wt. % zinc, other elements each in an amount of not greater than 0.05 wt. %, and other elements in a total amount of not greater than 0.15 wt. %, based on the total weight of the improved aluminum alloy.

20. The method of claim 13, wherein the 300 series aluminum alloy is obtained from recycled road wheels.