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This paper reviews the current state of metallographic development as applied to mechancially alloyed AL 9021 and furthers the understanding of mechanical alloys in general. Also presented is a scanning electron microscope (SEM) technique for accurately and efficiently determining grain size in this ultrafine-grained material. Considerable skill is required on the part of the metallographer due to the high magnifications that must be used with the SEM. Care must be taken not to overetch the material, or large errors in grain size measurement will occur. Various etchants were examined and results from the one providing the best detail are described. The effect of overaging on the microstructure is presented along with the unusual precipitation reactions that take place. The key to gaining a better understanding of the unique structure and properties of mechanical alloys lies in the use of high magnification metallography.
mechanical alloys, etchants, grain size determination, internal cracking, shear ridges, aging, microstructure, microstructural changes, oxygen evolution, microsuperplasticity, metallography, metallurgical specimens, metallographic techniques
Professor, University of Calgary, Calgary, Alberta