High Strain Rate Superplasticity in Some Lightweight Alloys and Their Composites

Abstract

Over the last decade, superplasticity at high strain rates (>10⁻¹ s⁻¹) has been reported in many fine grain structural materials, including metal-matrix composites, mechanically-alloyed materials, and modified conventional alloys. Up to date, there exists extensive data indicating superplastic strain rate increases with decreasing grain size. However, some recent experimental evidences also suggest that the presence of a small amount of liquid phase at interfaces or grain boundaries can influence the deformation mechanisms and enhance the strain rate for superplasticity. In the present paper, two alloy systems- 2124 Al and ZK60 Mg, and their metal matrix composites are examined. Microstructure-superplastic property relations for each alloy and its composite are characterized and compared to illustrate the optimal microstructural and testing conditions for achieving highstrain-rate superplasticity.