Severe plastic deformation as a processing tool for developing superplastic metals

Processing through the imposition of severe plastic deformation (SPD) provides an opportunity to achieve significant grain refinement in metallic alloys. Typically, the materials processed in this way have grain sizes in the submicrometer or the nanometer range. This paper describes the application of SPD processing through the procedure of Equal-Channel Angular Pressing (ECAP) in which a metal is pressed through a die constrained within a channel that is bent through an abrupt angle generally equal to, or very close to, 90°. Provided these ultrafine grain sizes are reasonably stable at high temperatures, these materials are capable of exhibiting very significant superplastic ductilities when pulled in tension at elevated temperatures. Typical examples of this superplastic behavior are presented for several aluminum-based alloys and for a magnesium alloy.