High-Strength Aluminum P/M Alloys

Powder metallurgy (P/M) technology provides a useful means of fabricating net-shape components that enables machining to be minimized, thereby reducing costs. Aluminum P/M alloys can therefore compete with conventional aluminum casting alloys, as well as with other materials, for cost-critical applications. In addition, P/M technology can be used to refine microstructures compared with those made by conventional ingot metallurgy (I/M), which often results in improved mechanical and corrosion properties. Consequently, the usefulness of aluminum alloys for high-technology applications, such as those in aircraft and aerospace structures, is extended.

Aluminum alloys have numerous technical advantages that have enabled them to be one of the dominant structural material families of the 20th century. Aluminum has low density (2.71 g/cm3) compared with competitive metallic alloy systems. It also has good inherent corrosion resistance because of the continuous, protective oxide film that forms very quickly in the air, and good workability that enables aluminum and its alloys to be economically rolled, extruded, or forged into useful shapes.

Major alloying additions to aluminum such as copper, magnesium, zinc, and lithium - alone, or in various combinations - enable aluminum alloys to attain high strength. Designers of aircraft and aerospace systems generally like to use Aluminum alloys because they are reliable, reasonably isotropic and low in cost compared to more exotic materials such as organic composites.

Aluminum alloys do have limitations compared with competitive materials. For example, Young`s modulus of aluminum (about 70 GPa, or 10 x 106 psi) is significantly lower than that of ferrous alloys (about 210 GPa, or 30 x 106 psi) and titanium alloys (about 112 GPa, or 16 x 106 psi). This lower modulus is almost exactly offset by the density advantage of aluminum compared to iron- and titanium-base alloys. Nevertheless, designers could exploit higher-modulus aluminum alloys in many stiffness-critical applications.

Aluminum P/M Processing

There are several steps in aluminum P/M technology that can be combined in various ways, but they will be conveniently described in three general steps:

    * Powder production
    * Powder processing (optional)
    * Degassing and consolidation.

Powder can be made by various RS processes including atomization, splat quenching to form particulates, and melt spinning to form ribbon. Alternatively, powder can be made by non-RS processes such as by chemical reactions including precipitation or by machining bulk material.

Powder-processing operations are optional and include mechanical attrition (for example, ball milling) to modify powder shape and size or to introduce strengthening features, or comminution such as that used to cut melt-spun ribbon into powder flakes for subsequent handling.

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