Effects of strain rate and test temperature on flow behaviour and microstructural evolution in AA 8090 Al–Li alloy

Abstract

Tensile specimens of superplastic forming grade AA 8090 Al–Li alloy were deformed at constant strain rates in the range 1×10-5–1×10-2 s-1 and at constant temperatures in the range 298–843 K, to investigate their effects on the nature of stress–strain (cσ–ε curves and on the concurrent microstructures, substructures, and microtextures. The σ–ε curves exhibited flow hardening in the early part of deformation, the rate of which was found to increase with an increase in strain rate and decrease in temperature. Grain growth, cavitation, dislocation interactions, and texture weakening were observed to occur during superplastic deformation. The early part of deformation involved a substantial dislocation slip contribution to flow hardening and to the mechanism for superplastic flow. However, the microstructural evolution facilitated the conventional mechanism of grain boundary sliding and its accommodation by the diffusional process, as suggested by the strain rate sensitivity index and activation energy determined.