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.