On the advantages of using powder metallurgy in new light metal alloy design

Historically, the production of metallic components for the automotive and aerospace industries has been dominated by wrought and ingot metallurgy metal forming practices. These technologies offer considerable design flexibility to engineers and are readily amenable to ferrous and nonferrous alloys alike. However, in applications that require precise dimensional control, the tolerances attainable are generally inadequate. This represents a formidable limitation and mandates the incorporation of expensive secondary machining. Furthermore, because these processes are carried out under conditions that approach those of equilibrium, these technologies are also faced with rather strict limitations on the range of alloy chemistries that can be employed. As the demands for improved material performance and process economics increase, the aforementioned shortcomings become increasingly important. Consequently, considerable attention has and continues to be focused on alternate metal forming techniques such as powder metallurgy (P/M). Using the P/M approach, dimensional tolerances are commonly improved by one to two orders of magnitude and alloy chemistry limitations are essentially eliminated. The work described herein provides an overview of select P/M techniques developed by the authors, initially to enhance the hardness and tensile properties of aluminum-based P/M alloys through a mineral dissociation/diffusion process. This is expanded through alloy development research wherein a P/M processing route designed to simulate industrial practices is used in the most recent work based on the effects of rare earth additions on selected mechanical properties of aluminum P/M alloys. These results include a compilation of theoretical calculations (thermodynamics and diffusion rates) that are supported by experimental data using techniques that include electron microprobe analyses, X-ray diffraction, tensile testing, and wear testing. Specific findings are that minerals/compounds such as wollastonite and silver nitrate can be successfully reacted to enhance selected mechanical properties of aluminum P/M alloys and that wear resistance may be improved through a P/M approach applied to AA2014. This article is based on a presentation made in the symposium entitled “Fourth International Alloy Conference,” which occurred in Kos. Greece, from June 26 to July 1, 2005, and was sponsored by Engineering Conferences International (ECI) and co-sponsored by Lawrence Livermore National Laboratory and Naval Research Laboratory, United Kingdom.