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Aluminum alloys produced by powder metallurgy (PM) processing have the potential to solve many material problems in aerospace systems. However, to optimize fully the performance of these materials, strict processing control is required. For example, the breakup and redistribution of oxides, which is key to achievement of maximum properties, is directly related to vacuum degassing, hot pressing, and subsequent working of the material. An analysis of each of these steps is reviewed for aluminum PM Alloy 7091 with respect to oxide breakup and distribution.

Dispersion-strengthened powder metallurgy aluminum alloys are being developed for structural applications up to 616 K (650°F). This research is being conducted under Air Force Wright Aeronautical Laboratories/Materials Laboratory Contract No. F33615-81-C-5096. The Lockheed-California Co. is the prime contractor with the Aluminum Company of America (Alcoa) and Pratt and Whitney Aircraft participating as subcontractors. The current alloy development has been directed towards the goal of producing high-strength/high-stiffness alloys with properties competitive to those of Ti-6Al-4V on a density-compensated basis. Alcoa has been developing the Al-Fe-Ce alloy system and Pratt and Whitney the Al-Fe-Mo alloy system. The second iteration of alloy development is presented. Mechanical property behavior of each rectangular extruded alloy was evaluated. The testing included room-temperature and elevated-temperature tension, fracture toughness, creep, and elevated-temperature stability tests. The Al-Fe-Ce alloys met or exceeded most of the program goals, while the Al-Fe-Mo alloys nearly achieved all of the goals. Achievement of the target properties provides a 15% weight savings for airframe structures and up to 35% weight savings for engine components.

Current U.S. Air Force programs are using aluminum powder metallurgy (PM) to extend the use of aluminum in both airframe and engine applications. The benefits of aluminum PM over conventional ingot metallurgy (IM) processing include enhanced mechanical properties resulting from a very homogeneous microstructure, extension of solid solubility limits, formation of metastable phases, and decreased grain size. During processing of the aluminum powder into a final product or into a workable preform, degassing is desirable to facilitate the breakup of the oxide skin and to disperse it. Also, the undesirable hydroxides that form must be removed to optimize mechanical properties. Although degassing has been frequently studied, evaluation techniques for degassing efficiency have been neglected. This program deals with the development of an effective and rapid method of evaluating degassing in aluminum products. Several methods, including ultrasonic inspection, density measurements, mass spectroscopy, and optical metallography, have been studied and evaluated using 7091 alloy small laboratory compacts. The times and temperatures of degassing were varied in such a way as to ensure that both adequate and poor degassing conditions were obtained. Each method of evaluation is discussed.