Superplastic behaviour in aluminium-lithium alloy 8090

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The present work has examined and compared microstructural evolution and superplastic behaviour in two aluminium-lithium (8090) sheet alloys. these have been processed to develop fine grain microstructures by either static recrystallisation, prior to superplastic forming (spf), or by strain induced in-situ, or dynamic, recrystallisation during the early stages of deformation. it was observed that the dynamically recrystallised material had a higher potential for superplastic flow than the statically recrsytallised material. this was attributed to the small grain structure developed during the initial stages of superplastic deformation, and which remained relatively stable during deformation. additionally, the resistance to neck prœpogation was due to the contribution of both strain-rate sensitivity of flow stress and work hardening. it was noted that for the dynamically recrystallising alloy further ductility enhancement could be achieved by the control of the strain-rate path. a rapid pre-strain improved significantly the subsequent superplastic elongation to failure at the optimum strain-rate. further enhancement has been obtained by rapid prestraining at constant velocity, followed by deformation to failure at lower constant velocity.