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 costcritical 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. This article describes and reviews the latter of these two areas of aluminum P/M technology where high strength and improved combinations of properties are obtained by exploiting the inherent advantages of P/M for alloy design. The metallurgical reasons for the microstructural refinement made possible by P/M are discussed. The two broad high-strength P/M technologies--rapid solidification (RS) and mechanical attrition (mechanical alloying/ dispersion strengthening)---are described. The various steps in aluminum P/M technology are explained to produce an appreciation for the interrelationship between powder processing and resultant properties. Finally, the major thrust areas of P/M alloy design and development are reviewed and some properties of the leading aluminum P/M alloys discussed. No attempt is made to provide design-allowable mechanical properties, and the data presented for the various P/M alloys may not be directly comparable because of differences in product forms. Nevertheless, the properties presented will enable the advantages of aluminum P/M alloys to be appreciated. Greater details of aluminum P/M alloys are provided in other reviews (Ref 1 to 7). Conventional pressed and sintered aluminum P/M alloys for less demanding applications are described in the Appendix to this article.