The invention relates generally to a tempered aluminum alloy casting, a method of forming the tempered aluminum alloy casting, an automotive vehicle component formed of the tempered aluminum alloy casting, and a method of manufacturing the component.
Tempered aluminum alloy castings are oftentimes used in the automotive industry to form lightweight components, including complex structural, body-in-white, suspension, and chassis components. Oftentimes, it is desirable to use cast aluminum alloys having an elongation of at least 8%, for example when the cast aluminum alloy is subjected to a self-piercing rivet (SPR) process. A cast aluminum alloy having an elongation of at least 9 to 10% can be achieved by an aluminum alloy known as “Aural 2” in the heat treated T7 condition. However, when this type of aluminum alloy is used, the tempering process typically requires a T7 heat treatment cycle, solution heat treating, air quenching, straightening with a coining, and artificial aging. Thus, the use of the Aural 2 alloy and the associated process is limited due to the cost of the operations. It is desirable to achieve an aluminum alloy casting having a minimum elongation of 8%, before any heat treatment or paint oven exposure of the cast aluminum alloy, which can be subjected to self-piercing rivets, and a less costly tempering process.
One aspect of the invention provides an aluminum alloy, comprising: silicon in an amount of 4.0 to 9.0 weight percent (wt. %), copper in an amount up to 0.10 wt. %, iron in an amount up to 0.25 wt. %, manganese in an amount of 0.3 to 0.60 wt. %, magnesium in an amount of 0.10 to 0.60 wt. %, titanium in an amount up to 0.15 wt. %, strontium in an amount of 0.01 to 0.60 wt. %, and a balance of aluminum, except for possible incidental elements and/or impurities, based on the total weight of the aluminum alloy. The aluminum alloy is cast, and a coating is applied to the aluminum alloy.
Another aspect of the invention provides a method of manufacturing a cast aluminum alloy. The method comprises the steps of: casting an aluminum alloy, the aluminum alloy including silicon in an amount of 4.0 to 9.0 weight percent (wt. %), copper in an amount up to 0.10 wt. %, iron in an amount up to 0.25 wt. %, manganese in an amount of 0.3 to 0.60 wt. %, magnesium in an amount of 0.10 to 0.60 wt. %, titanium in an amount up to 0.15 wt. %, strontium in an amount of 0.01 to 0.60 wt. %, and a balance of aluminum, except for possible incidental elements and/or impurities, based on the total weight of the aluminum alloy; applying a coating to the cast aluminum alloy; and heating the coated cast aluminum alloy.
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:
One aspect of the invention provides a tempered aluminum alloy casting, and a thermally stable component formed of the tempered aluminum alloy casting. Another aspect of the invention includes a method of manufacturing the tempered aluminum alloy casting, and a thermally stable component formed of the tempered aluminum alloy casting. Typically, the aluminum alloy has an elongation of at least 8%, or at least 9 to 10% after casting (F temper condition), which can be tested according to the ASTM E8 tensile testing specification, and the cast aluminum alloy is then subjected to an artificial aging (T5) process. The F temper condition is with no heat treatment. The T5 process includes cooling from an elevated temperature shaping process then artificially aging.
The aluminum alloy preferably leaves a casting facility or foundry in the as-cast (F temper) condition with an elongation of at least 8% or at least 10%, when tested according to the ASTM E8 specification, which is the preferred minimum elongation for next subjecting the cast aluminum alloy to a self-piercing rivet (SPR) process. The cast aluminum alloy can then be shipped to another entity or manufacturer, such as an OEM or customer. The artificial aging process on the cast aluminum alloy can be conducted at the OEM or customer's facility, for example on the OEM's paint line and/or at an ecoat sub-supplier and then shipped to an OEM, depending on the corrosion strategy for the component, rather than at the casting facility. The components that can be formed from the tempered aluminum alloy castings include lightweight automotive vehicle components. Examples of the components include structural, body-in-white, suspension, or chassis components or components, such as, but not limited to, a front shock tower, front body hinge pillar, tunnel, rear rail, door inner panel, door mirror bracket, cross car beam, inner and outer torque boxes, rear shock mount, etc.
The method used to form the component using the tempered aluminum alloy casting is typically less costly than a comparative method which includes a T7 heat treatment cycle. The comparative T7 heat treatment cycle includes solution heat treating for 60 minutes at 860° F. (460° C.)) of the Aural 2 or C65K aluminum alloy, air quenching the aluminum alloy at a rate of 4° C. per second (7.2° F. per second), straightening the aluminum alloy with a coining process, and artificial aging of the aluminum alloy between 60 and 140 minutes at 419° F. (215° C.). The reduced costs are achieved in part by using an aluminum alloy which is less costly than the comparative alloys Aural 2 and C65K.
The aluminum alloy used to form the reduced cost tempered aluminum alloy casting typically includes silicon in an amount of 4.0 to 9.0 weight percent (wt. %), copper in an amount up to 0.10 wt. %, iron in an amount up to 0.25 wt. %, manganese in an amount of 0.3 to 0.60 wt. %, magnesium in an amount of 0.10 to 0.60 wt. %, titanium in an amount up to 0.15 wt. %, strontium in an amount of 0.01 to 0.60 wt. %, and a balance of aluminum, except for possible incidental elements and/or impurities, based on the total weight of the aluminum alloy. According to example embodiments, the aluminum alloy casting comprises one of the alloys having a compositions within the ranges disclosed in Table 1, which are referred to as C611 and Aural 5S. The balance of both alloys includes aluminum, except for possible incidental elements and/or impurities. These two alloys resemble one another but have slightly different chemical compositions. Table 2 includes additional example ranges for the aluminum alloys. The ranges can be used in any combination. For example, a minimum amount of an element from Table 1 can be used with a maximum amount listed in Table 2, and/or a minimum amount of an element from Table 2 can be used with a maximum amount listed in Table 1. In addition, a minimum or maximum amount of an element of the C611 alloy composition of Table 1 or Table 2 can be used in combination with a minimum or maximum amount of the Aural 5S alloy composition of Table 1 or Table 2, and vice versa.
The less costly method used to form the component from the thermally stable tempered and cast aluminum alloy typically includes melting the aluminum alloy, casting the aluminum alloy, and possibly trimming the aluminum alloy. After the casting step, the cast aluminum alloy has an elongation of at least 8%, or at least 9 to 10%, which is preferred for self-piercing rivet processes. Thus, the method typically includes piercing the cast aluminum alloy. The method can further include deburring, surface grinding, and/or machining the cast aluminum alloy. After the casting and possible additional steps described above, the cast aluminum alloy can be shipped or otherwise transferred from the casting facility to another facility or location, such as to an OEM. After shipping the cast aluminum alloy, the method preferably includes the artificial aging process. This process typically includes applying a coating to the cast aluminum alloy, which is in the as-cast (F temper) condition, by an electrodeposition coating process, and curing the coating on the cast aluminum alloy to form the finished tempered component. For example, the OEM's existing electrodeposition coating process and paint bake oven can be used. The additional costly production steps of the comparative method described above are not required. Thus, the component formed from the tempered aluminum alloy casting is typically less costly to manufacture and is thermally stable. The reduced costs required to make the component can be achieved in part by using the electrodeposition coating process and the paint bake oven that already exists in operation at the OEM or another entity's assembly plant.
It is noted that the as-cast temper condition of the cast aluminum alloy is also referred as F—temper and/or foundry temper (more generally as-cast and/or as-fabricated). It is also referred to as the properties of the aluminum alloy casting without any post processing heat treatment. The mechanical properties of the as-cast aluminum alloy made with one of the Aural series of alloys (such as Aural 2, C65k, Aural 5S, or C611) change slightly over time after casting, but also stabilize after a certain period. This is known as natural aging. The lowest cost castings available are F temper, which is no heat treatment.
The electrodeposition coating process, such as the OEM or customer's existing process, can include a cross between plating and painting. Typically, electrodeposition coating processes are used for corrosion mitigation. According to one embodiment, the cast aluminum alloy is immersed in a water-based solution containing a paint emulsion. The coating thickness is limited by the voltage applied to the water-based solution. Since the coating is essentially liquid paint, once it has coated the cast aluminum alloy, a curing cycle is typically required at particular curing times and temperatures. The curing step is preferably conducted in an oven, such as a paint bake oven already used in production. The conditions of the curing cycle, such as curing time and temperature, can be determined in part by the chemistry of the coating. Since the chemistry of the electrodeposition coating can be provided by a chemical cross-linking process, the full cure typically requires both time and temperature to obtain the optimum coating properties. Multiple curing cycles, including heating for periods of time followed by cooling for periods of time, are typically repeated several times. However, these cure cycles can vary, for example from OEM to OEM, and even in different lines within the same OEM. After the F temper casting has been coated with the electrodeposition coated by itself and received, the electrodeposition cure is referred to as a T84. After the casting has completed the entire assembly process, and gone through all of the remaining paint cure ovens, the final condition of the aluminum alloy casting is referred to as a T85. The mechanical properties of the finished T85 casting should be approximate to the properties of a T5 aluminum casting formed according to the conventional process, without having to use the conventional oven at the foundry.
Typically, the electrodeposition coating and curing steps include applying the coating, heating the coated cast aluminum alloy for a period of time, and then allowing the coated cast aluminum alloy to cool to room temperature for a period of time. These steps are typically repeated a plurality of times, for example four times. The steps can be conducted in an electrodeposition coating oven, a primer oven, and/or an enamel oven. In an example embodiment, the first two cycles can be conducted in an electrodeposition coating oven, the third cycle can be conducted in a primer oven, and the fourth cycle can be conducted in an enamel oven. Each heating step can include heating to temperatures ranging from 180° F. to 385° F. for 9 to 25 minutes.
According to an example embodiment, an epoxy-type electrodeposition coating is applied to the cast aluminum alloy and then cured at a curing temperature of 320° F. for 20 minutes or 315° F. for 15 minutes, depending on the chemistry of the coating. As with paints, the energy used to cure the electrodeposition coating will also typically depend, in part, on the size and geometry of the cast aluminum alloy.
As discussed above, the component formed of the tempered, cast aluminum alloy is thermally stable and can achieve mechanical properties suitable for automotive vehicle applications. The cast aluminum alloy typically has a yield strength (YS) ranging from 90 to 200 MPa, an ultimately tensile strength (UTS) ranging from 220 to 300 Mpa, and an elongation percentage (%) of 7.0% to 19% prior to any heat treatment of the cast aluminum alloy when tested according to the ASTM E8 specification. The cast aluminum alloy typically has a yield strength (YS) ranging from 100 to 220 MPa, an ultimately tensile strength (UTS) ranging from 230 to 320, and an elongation percentage (%) of 6.0% to 15% after coating the cast aluminum alloy and after curing the coating on the cast aluminum alloy.
Table 3 illustrates the yield strength, ultimate tensile strength, and elongation percent of the example C611 tempered cast aluminum alloy when tested in the form of 2.8 mm plates. The yield strength, ultimate tensile strength, and the elongation percent can all be tested according to the ASTM E8 tensile testing specification.
Table 4 illustrates the illustrates the yield strength, ultimate tensile strength, and elongation percent of the example C611 paint bake tempered cast aluminum alloy when tested in the form of 2.8 mm excised castings. The yield strength, ultimate tensile strength, and elongation percent can all be tested to the ASTM E8 specification.
As indicated above, the component formed of the tempered aluminum alloy casting is in a thermally stable condition after the reduced cost method. The thermally stable condition typically means there is no change in mechanical properties of the tempered aluminum alloy casting after a period of time. European manufacturers of automotive components typically require no change in mechanical properties after short term exposure to heat (1 hour at 400° F. (205° C.)) and after a long term exposure (1000 hours at 300° F. (150° C.)).
As stated above, the cast aluminum alloy typically has at least 8% or at least 10% elongation, which is preferred for riveting, and can be used to form the thermally stable component with reduced costs, relative to the comparative component and method which includes the use of the Aural 2 or C65K aluminum alloy. The Aural 2 or C65K aluminum alloy is known to be more expensive than the Aural 5S or C611 aluminum alloy due to the higher amount of silicon. Table 4 provides the composition of the Aural 2 and C65K aluminum alloys. The balance of the composition of Table 5 includes aluminum and possible incidental elements and/or impurities.
Several experiments were conducted to evaluate the properties of the cast aluminum alloy and the tempered aluminum alloy casting formed by the reduce cost method according to various example embodiments. The methods tested included the use of electrodeposition processes and paint bake ovens already in use at OEM plants and an artificial aging process. The aluminum alloys tested were the Aural 5S and C611 aluminum alloys. The graph of
One method used to form the samples tested includes an electrodeposition coating provided by a supplier, MetoKote. The MetoKote paint cure cycle (time and temperatures) are shown in
As indicated above, the method can include a paint bake treatment already existing at the OEM's facility. This process includes applying a coating and/or paint to the aluminum alloy casting, heating the coating aluminum casting for a first period of time, and allowing the coated aluminum casting to cool for a second period of time. The coating, heating, and cooling steps can be repeated several times. The heat curves shown in FIGS. 4 and 8A-8C are examples of the times and temperatures of the heating steps conducted at the different OEMs. The multiple heating steps, conducted after coating and/or painting, together provide the aluminum casting with mechanical properties approximately equivalent to the mechanical properties of an aluminum casting after an artificial age T5 heat treatment at a foundry.
In this case, the aluminum alloy leaves the foundry in the as-csat (F temper) condition and has extra ductility, making the self-piercing riveting process easier. The aluminum alloy castings can then be subjected to an artificial aging (T5) treatment at the OEM paint line, versus at the casting factility. These steps are referred to as a T85 (paint bake) heat treatment. Due to the elimination of a heat treatment step, typical profile tolerances can be achieved without a secondary straightening process.
In
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 claims.
This PCT International Patent Application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/462,598 entitled “Process For Low-Cost Tempering Of Aluminum Casting”, filed Feb. 23, 2017, the entire disclosure of the application being considered part of the disclosure of this application, and hereby incorporated by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/US2018/019432 | 2/23/2018 | WO | 00 |
Number | Date | Country | |
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62462598 | Feb 2017 | US |