BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to bi-metal bearings for automotive applications, such as those including aluminum-based alloys, and methods of forming the same.

2. Related Art

[0002] Bearings for automotive engine applications are oftentimes formed of a bi-metal material including a base layer formed of an aluminum alloy attached to a backing layer formed of steel or a steel alloy. Certain applications require the base layer to provide high fatigue strength and good conformability, which existing materials may not be able to achieve.

SUMMARY OF THE INVENTION

[0003] One aspect of the invention provides a precipitation hardenable aluminum alloy for a bearing used in automotive engine applications. The aluminum alloy comprises copper, tin, magnesium, silicon, vanadium, and a balance of aluminum. The aluminum alloy of the present invention can be used in place of aluminum alloys of existing bi-metal bearing applications which do not provide adequate strength. The aluminum alloy of the present invention also provides the potential for OEMs to manufacture a smaller bearing architecture.

[0004] Another aspect of the invention provides a bearing comprising a base layer bonded to a backing layer. The base layer is formed of an aluminum alloy including a mixture of copper, tin, magnesium, silicon, vanadium, and a balance of aluminum. The base layer also includes a plurality of Mg ₂ Si precipitates. The base layer provides an exceptional combination of strength and ductility, and thus is ideal for bearings which require high fatigue strength and good conformability.

[0005] Another aspect of the invention provides a method of forming a bearing. The method includes providing a base layer formed of an aluminum alloy including a mixture of copper, tin, magnesium, silicon, vanadium, and a balance of aluminum; and bonding the base layer to a backing layer. The method further includes heat treating the base layer after bonding the base layer to the backing layer to form a plurality of Mg ₂ Si precipitates in the base layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] 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:

[0007] Figure 1 is a perspective view of an engine bearing constructed according to an exemplary embodiment the present invention;

[0008] Figure 2 is a flow diagram illustrating a method of forming a bearing according to an exemplary embodiment of the present invention;

[0009] FIG. 3 is an enlarged fragmentary cross-sectional view of the bearing of Figure 1 showing the backing layer and the base layer; and

[0010] Figure 4 is an enlarged fragmentary cross-sectional view of the bearing of Figures 1 and 3 with an additional layer applied to the base layer. DESCRIPTION OF THE ENABLING EMBODIMENT

[0011] The invention provides a bearing 20 for an automotive engine application having an exceptional combination of fatigue strength and conformability. An example of the bearing according to one embodiment is shown in Figure 1. The bearing 20 generally comprises a base layer 22 formed of a heat treated, precipitation hardened, aluminum alloy including a plurality of Mg ₂ Si precipitates 24. The bearing 20 is preferably formed by casting roll casting the aluminum alloy to form the base layer 22, hot bonding the base layer 22 to a backing layer 26, and then heat treating the base layer 22 bonded to the backing layer 26. Figure 2 is a flow diagram of method steps used to form the bearing 20 according to one exemplary embodiment.

[0012] The aluminum alloy used to form the base layer 22 preferably includes a mixture of copper (Cu), tin (Sn), magnesium (Mg), silicon (Si), vanadium (V), and a balance of aluminum (Al). The vanadium present in the aluminum alloy raises the recrystallization temperature and inhibits grain grown at elevated temperatures. The alloying elements could be added in various different amounts, but the amount of vanadium is typically smaller than the amounts of the other elements. For example, if the copper, tin, magnesium, and silicon are each present in an amount of 5 weight percent, based on the total weight of the aluminum alloy, then the vanadium is present in an amount less than 5 weight percent. In addition, the majority of the composition of the alloy typically consists of aluminum.

[0013] Other alloying elements could be included in the aluminum alloy, as long as they do not interfere with the desired amount or size of the Mg ₂ Si precipitates 24. In one exemplary embodiment, the aluminum alloy is initially formed by extruding aluminum, adding the alloying elements to the aluminum, and casting the aluminum alloy to provide the base layer 22. The alloying elements are typically added to the aluminum during the casting process. In the exemplary embodiment, the casting process includes roll casting, but could alternatively include another type of casting, such as belt casting.

[0014] Next, the base layer 22 is bonded to the backing layer 26. The backing layer 26 is typically formed of steel or a steel alloy. The bonding step typically includes hot bonding by heating at least one of the base layer 22 and/or the backing layer 26 to a temperature ranging from 315 to 425° C, and then pressing the base layer 22 and the backing layer 26 together. However, other methods can be used to bond the base layer 22 to the backing layer 26, for example a cold bonding process.

[0015] Once the base layer 22 is bonded to the backing layer 26, the base layer 22 is heat treated to form the Mg ₂ Si precipitates 24. During the heat treatment, the growth of the Mg ₂ Si precipitates 24 within the aluminum matrix is controlled in attempt to achieve the desired amount and size of the Mg ₂ Si precipitates 24. It is oftentimes preferred to have a greater number of precipitates 24 which are smaller in size than a fewer number of precipitates 24 which are larger in size, even if the total volume of precipitates 24 is greater in the latter case. The Mg ₂ Si precipitates 24 also preferably have good coherency, which may be more difficult to achieve with the smaller precipitates 24. The heat treatment could also form CuAl ₂ precipitates and Si precipitates. However, the Mg ₂ Si precipitates 24 are more effective at hardening the base layer 22 in smaller amounts, compared to the CuAl ₂ precipitates and Si precipitate. In certain embodiments, the aluminum alloy of the base layer 22 can be referred to as a 6000 series aluminum alloy after the heat treat- ment step. 6000 series aluminum alloy specifies a group of aluminum alloys that contains both magnesium and silicon as the primary alloying elements. The magnesium levels for these alloys range from 0.20 wt.-% to 3.0 wt.-%, and silicon levels range from 0.2 wt.-% to 1.8 wt.-%. Further elements included are Fe, Cu, Mn. Particularly Fe can be present in the alloy in an amount of from 0,05wt.-% to 1 wt.-%, Cu in an amount of from 0,01 wt.-% to 1,2 wt.-% and Mn in amount of from 0,03 wt.-% to 1,4 wt.-%. Optionally, micro-alloying elements selected from the group consisting of B, Bi, Cr, Ni, Pb, Sn, Sr, Ti, V, Zn and Zr can be present in the aluminum alloy.

[0016] The heat treatment step typically includes heating the base layer 22 bonded to the backing layer 26 in a fluidized bed. In the exemplary embodiment, this step includes heating the base layer 22 bonded to the backing layer 26 to a temperature of 515° C in a solution contained in the fluidized bed for one hour, followed by quenching the base layer 22 bonded to the backing layer 26 in water. This particular type of heat treatment is typically referred to as a T4 temper process. Alternatively, a T6 temper process can be used, which includes heating the base layer 22 bonded to the backing layer 26 to a temperature of 175° C in the solution contained in the fluidized bed for eight hours. However, the aluminum alloy typically achieves a greater hardness and strength when the T4 temper process is used. The ductility of the aluminum alloy is also greater in the T4 condition.

[0017] Alternatively, other techniques can be used to heat treat the base layer 22 once it is bonded to the backing layer 26. In one embodiment, the heat treating step includes heating the base layer 22 bonded to the backing layer 26 in a salt bath. In another embodiment, the heat treating step includes heating the base layer 22 by induction heating. In yet another embodiment, the heat treating step includes heating the base layer 22 using a laser. In each case, the growth of the Mg ₂ Si precipitates 24 is controlled in attempt to achieve the desired amount and size of the Mg ₂ Si precipitates 24, as well as good coherency. Figure 3 shows the base layer 22 with the Mg ₂ Si precipitates 24 after the heat treatment.

[0018] Once the heat treatment step is complete, the base layer 22 including the Mg ₂ Si precipitates 24 has an exceptional combination of strength and ductility. One or more additional layers 28 may be applied to the base layer 22 to enhance performance of the bearing 20. For example, another metal-based layer or a polymer-based coating may be applied to the base layer 22 to provide additional wear resistance, strength, and/or seizure resistance. Figure 4 shows an example of the base layer 22 of Figures 1 and 3 with an additional layer 28 applied to the base layer 22.

[0019] 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 appended claims.