LOW COST HIGH DUCTILITY CAST ALUMINUM ALLOY

Abstract

An aluminum alloy for casting into a component, such as a vehicle component, is provided. The aluminum alloy includes silicon, zinc, magnesium, copper, manganese, iron, and strontium. After the casting step, the cast aluminum alloy has a yield strength of at least 105 MPa, ultimate tensile strength (UTS) of at least 180 MPa, and an elongation of 8% to 10%.

Description

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, 6.0 to 8.0 wt. % silicon, 1.0 to 2.0 wt. % zinc, less than 0.25 wt. % iron, and 0.2 wt. % to 0.4 wt. % manganese, based on the total weight of the aluminum alloy.

Another aspect of the invention provides an aluminum alloy, comprising at least 80 weight percent (wt. %) aluminum, 6.0 to 8.0 wt. % silicon, 1.0 to 2.0 wt. % zinc, 0.3 to 0.6 wt. % iron, and 0.2 wt. % to 0.5 wt. % manganese, based on the total weight of the aluminum alloy.

Yet another aspect of the invention provides an aluminum alloy, comprising at least 80 weight percent (wt. %) aluminum, 9.5 wt. % to 11.5 wt. % silicon, 0.3 wt. % to 0.8 wt. % zinc, 0.3 to 0.6 wt. % iron, and 0.2 wt. % to 0.5 wt. % manganese, based on the total weight of the aluminum alloy.

Another aspect of the invention provides a cast aluminum alloy formed of at least one of the aluminum alloys disclosed above, and a method of manufacturing the cast aluminum alloy.

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

FIG. 2 illustrates examples of the aluminum alloy and cast parts formed of the aluminum alloy according to example embodiments;

FIG. 3 illustrates mechanical properties of the aluminum alloy according to an example embodiment of the invention relative to a comparative aluminum alloy;

FIG. 4 is a bending curve (load v. extension) comparing the aluminum alloy according to an example embodiment of the invention relative to a comparative aluminum alloy; and

FIG. 5 illustrates the results of a rivetability test comparting the aluminum alloy according to an example embodiment of the invention relative to a comparative 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. Examples of components 10 formed of the aluminum alloy according to example embodiments is shown in FIGS. 1 and 2.

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. The aluminum alloy also includes an amount of silicon (Si), which helps achieve improved castability of the aluminum alloy and thus reduces a scrap rate and reduces costs. Besides the large amount of silicon eutectic phase, the elongation of the component formed of the aluminum alloy is typically 5% to 8%. The castability, strength, and toughness of the aluminum alloy can also be adjusted based on the amount of silicon.

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. Strontium (Sr) can also be added to modify properties that occur due to the silicon.

According to a first example embodiment, in addition to at least 80 wt. % aluminum, the aluminum alloy includes 6.0 to 8.0 wt. % silicon, 1.0 to 2.0 wt. % zinc, 0.05 to 0.3 wt. % magnesium, less than 0.05 wt. % copper, 0.2 wt. % to 0.4 wt. % manganese, less than 0.25 wt. % iron, and 0.03 wt. % to 0.08 wt. % strontium, based on the total weight of the aluminum alloy. The aluminum alloy can also include other elements, for example impurities, each in an amount of less than 0.05 wt. % and in a total amount of less than 0.15 wt. %, based on the total weight of the aluminum alloy. The aluminum alloy of the first example embodiment is referred to as Aural 5M because it is a modified version of Aural 5S.

According to a second example embodiment, in addition to at least 80 wt. % aluminum, the aluminum alloy includes 6.0 to 8.0 wt. % silicon, 1.0 to 2.0 wt. % zinc, 0.05 to 0.3 wt. % magnesium, 0.10 wt. % to 0.40 wt. % copper, 0.2 wt. % to 0.5 wt. % manganese, 0.3 wt. % to 0.6 wt. % iron, 0.01 wt. % to 0.03 wt. % strontium, and 0.15 wt. % maximum titanium, based on the total weight of the aluminum alloy. The aluminum alloy can also include other elements, for example impurities, each in an amount of less than 0.05 wt. % and in a total amount of less than 0.15 wt. %, based on the total weight of the aluminum alloy. The aluminum alloy of the second example embodiment is referred to as Aural 5R because it includes a significant amount of recycled materials. Examples of cast components 10 formed of the aluminum alloys containing recycled materials are shown in FIG. 2.

According to a third example embodiment, in addition to at least 80 wt. % aluminum, the aluminum alloy includes 9.5 to 11.5 wt. % silicon, 0.3 wt. % to 0.8 wt. % zinc, 0.1 to 0.6 wt. % magnesium, 0.20 wt. % to 0.90 wt. % copper, 0.2 wt. % to 0.5 wt. % manganese, 0.3 wt. % to 0.6 wt. % iron, 0.01 wt. % to 0.03 wt. % strontium, and 0.15 wt. % maximum titanium, based on the total weight of the aluminum alloy. The aluminum alloy can also include other elements, for example impurities, each in an amount of less than 0.05 wt. % and in a total amount of less than 0.15 wt. %, based on the total weight of the aluminum alloy. The aluminum alloy of the third example embodiment is referred to as Aural 2R because it includes a significant amount of recycled materials.

The aluminum alloys of Examples 1-3 are provided in Table 1 below.

	TABLE 1
									Other	Other
	Si	Zn	Mg	Cu	Mn	Fe	Sr	Ti	Each	Total
Ex. 1 Aural 5M	6.0-8.0	1.0-2.0	0.05-0.30	<0.05	0.20-0.40	0.25	0.03-0.08		0.05	0.15
Ex. 2 Aural 5R	6.0-8.0	1.0-2.0	0.05-0.30	0.10-0.40	0.2-0.5	0.3-0.6	0.01-0.03	0.15	0.05	0.15
								maximum
Ex. 3 Aural 2R	9.5-11.5	0.3-0.8	0.1-0.6	0.20-0.90	0.2-0.5	0.3-0.6	0.01-0.07	0.15	0.05	0.15
								maximum

The aluminum alloy of examples 2 and 3 is preferable obtained from recycled aluminum, such as recycled road wheels. The energy required to produce the aluminum alloy is reduced by about 95% when the aluminum alloy is formed from recycled materials.

Another aspect of the invention provides the cast component 10 formed of the aluminum alloy, and a method of manufacturing the cast component 10 by melting and casting the melted aluminum alloy. The method of forming the cast component typically begins by melting the aluminum alloy. Any casting process used to form components, 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.

After the casting the aluminum alloy of example 1 (Aural 5M) and after either artificial age (T5 temper) or exposing the cast aluminum alloy to a body shop paint bake cycle, the cast aluminum alloy has a yield strength of at least 100 to 120 MPa, ultimate tensile strength (UTS) of at least 180 MPa, and an elongation of 5% to 7%. The cast Aural 5M in the as-cast (F temper) condition has a yield strength of at least 105 MPa to 110 MPa, ultimate tensile strength (UTS) of at least 180 MPa, and an elongation of 8% to 15%.

An example of the aluminum alloy of the second example embodiment, Aural 5R, has a higher amount of recycled (secondary materials). After casting, the aluminum alloy is either artificially aged (T5 temper) or exposed to a body shop paint bake cycle, and thus the cast aluminum alloy has a yield strength of at least 140 to 150 MPa, ultimate tensile strength (UTS) of 270 MPa, and an elongation of 5% to 7%. The cast Aural 5R in the as-cast (F temper) condition has a yield strength of at least 110 MPa to 120 MPa, ultimate tensile strength (UTS) of 240 MPa, and an elongation of 8% to 10%.

An example of the aluminum alloy of the third example embodiment, Aural 2R, has a higher amount of recycled (secondary materials) and after casting is either artificial aged (T5 temper) or exposed to a body shop paint bake cycle, and thus the cast aluminum alloy has a yield strength of at least 140 to 150 MPa, ultimate tensile strength (UTS) of 290 MPa, and an elongation of 3% to 5%. The cast Aural 5R in the solution, forced air quench (4° C./sec) and artificially age (T7 temper) condition has a yield strength of at least 125 MPa to 130 MPa, ultimate tensile strength (UTS) of 200 MPa, and an elongation of 8% to 10%.

The aluminum alloy according to example embodiments provides for exceptional mechanical properties, corrosion resistance, rivetability, and castability. FIG. 3 illustrates the mechanical properties of the aluminum alloy of example 1 (Aural 5M) relative to a comparative aluminum alloy (Aural 5S). The yield strength, ultimate tensile strength, and elongation are tested using ASTM E8/E8M-21 (Standard Test Methods for Tension Testing of Metallic Materials). FIG. 4 is a bending curve (load v. extension) comparing the aluminum alloy of example 1 (Aural 5M) to the comparative aluminum alloy (Aural 5S). The composition of the comparative aluminum alloy (Aural 5S) includes at least 80 wt. % aluminum, 6.0 to 8.0 wt. % silicon, 0.1 to 0.6 wt. % magnesium, 0.4 wt. % to 0.6 wt. % manganese, 0.25 wt. % max iron, and 0.01 wt. % to 0.03 wt. % strontium, based on the total weight of the aluminum alloy. The test method used to obtain the bending curve is an adaptation based on a German Association of the Automotive Industry or VDA standard VDA 238-100 (Plate bending test for metallic materials). The VDA 238-100 standard is for 2.0 mm thick wrought products (sheet, etc.). Thus, the test is adapted to include castings. A correction factor is applied if the casting thickness is above 2.0 mm. FIG. 5 illustrates the results of a rivetability test comparing the aluminum alloy of example 1 (Aural 5M) to the comparative aluminum alloy (Aural 5S). The rivetability test included applying a self-piercing rivet to the aluminum alloy of example 1 (Aural 5M) and the comparative aluminum alloy (Aural 5S). The self-piercing rivet is a single-step technique which includes using a semi-tubular rivet to clinch sheets of the aluminum alloy together. The sheets are clamped between a die and blankholder, and the rivet is driven into the sheets between a punch and a die. The rivet pierces the top sheet and the die shape causes the rivet to flare within the lower sheet to form a mechanical interlock. The die shape causes a button to form on the underside of the tower sheet. Preferably, the rivet tail does not pierce though the button

Both the Aural 2R and Aural 5R compositions exhibit good corrosion resistance when subjected to a salt spray test for 100 hours according to ASTM B117-16 (Standard Practice for Operating Salt Spray (Fog) Apparatus).

The cast component 10 formed from the casting step can be, for example, a component for use in a vehicle. 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.

Generally, it takes up to 95 percent less energy to recycle than to produce primary aluminum, which reduces the carbon footprint of the foundries. The aluminum alloys of the present invention which include high amounts of recycled material, known as Aural 2R and Aural 5R (R=high amt of recycled material), will utilize both recycled clean crushed road wheels as well as wrought aluminum stamping offal. Development of these green aluminum alloys, using secondary recycled aluminum for BIW and structural components, will allow for both less cost of raw material, and a lower carbon footprint while still meeting stringent automotive industry standards. The cast components formed of the aluminum alloys have good rivetability and castability.

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

1. An aluminum alloy, comprising: at least 80 weight percent (wt. %) aluminum; 6.0 to 8.0 wt. % silicon; 1.0 to 2.0 wt. % zinc; less than 0.25 wt. % iron; and 0.2 wt. % to 0.4 wt. % manganese, based on the total weight of the aluminum alloy.

2. The aluminum alloy according to claim 1 further including 0.05 to 0.3 wt. % magnesium, less than 0.05 wt. % copper, and 0.03 wt. % to 0.08 wt. % strontium, based on the total weight of the aluminum alloy.

3. The aluminum alloy according to claim 2 further including other elements each in an amount of less than 0.05 wt. % and in a total amount of less than 0.15 wt. %, based on the total weight of the aluminum alloy.

4. A cast component formed of the aluminum alloy of claim 1.

5. The cast component of claim 4, wherein the cast aluminum alloy has a yield strength of at least 105 MPa to 110 MPa, ultimate tensile strength (UTS) of at least 180 MPa, and an elongation of 8% to 15%.

6. An aluminum alloy, comprising: at least 80 weight percent (wt. %) aluminum; 6.0 to 8.0 wt. % silicon; 1.0 to 2.0 wt. % zinc; 0.3 to 0.6 wt. % iron; and 0.2 wt. % to 0.5 wt. % manganese, based on the total weight of the aluminum alloy.

7. The aluminum alloy according to claim 6, further including 0.05 to 0.3 wt. % magnesium, 0.10 wt. % to 0.40 wt. % copper, 0.01 wt. % to 0.03 wt. % strontium, and not greater than 0.15 wt. % titanium, based on the total weight of the aluminum alloy.

8. The aluminum alloy according to claim 7 further including other elements each in an amount of less than 0.05 wt. % and in a total amount of less than 0.15 wt. %, based on the total weight of the aluminum alloy.

9. A cast component formed of the aluminum alloy of claim 6.

10. The cast component of claim 9, wherein the cast aluminum alloy has a yield strength of at least 110 MPa to 120 MPa, ultimate tensile strength (UTS) of at least 240 MPa, and an elongation of 8% to 10%.

11. An aluminum alloy, comprising: at least 80 weight percent (wt. %) aluminum; 9.5 to 11.5 wt. % silicon; 0.3 to 0.8 wt. % zinc; 0.3 to 0.6 wt. % iron; and 0.2 wt. % to 0.5 wt. % manganese, based on the total weight of the aluminum alloy.

12. The aluminum alloy according to claim 11 further including 0.1 to 0.6 wt. % magnesium, 0.20 wt. % to 0.90 wt. % copper, 0.01 wt. % to 0.07 wt. % strontium, and not greater than 0.15 wt. % titanium, based on the total weight of the aluminum alloy.

13. The aluminum alloy according to claim 12 further including other elements each in an amount of less than 0.05 wt. % and in a total amount of less than 0.15 wt. %, based on the total weight of the aluminum alloy.

14. A cast component formed of the aluminum alloy of claim 11.

15. The cast component of claim 14, wherein the cast aluminum alloy has a yield strength of at least 125 MPa to 130 MPa, ultimate tensile strength (UTS) of at least 200 MPa, and an elongation of 8% to 10%.