Continuous dynamic recrystallization during the transient severe deformation of aluminum alloy 7475

Effect of strain rate and its discontinuous changes on the deformation and microstructural behavior of a coarse-grained 7475 Al alloy were studied in multidirectional forging at 763 K. Deformation at a higher strain rate of 3 × 10^?2 s^?1, controlled by homogeneous dislocation motion, leads to partial grain refinement taking place only near the original grain boundaries. Deformation at a lower rate of 3 × 10^?4 s^?1, controlled mainly by grain boundary sliding, in contrast, results in full development of strain-induced grains through grain fragmentation due to microshear band formation. Under conditions of discontinuous changes in strain rate, the flow stresses and grain size developed by subsequent severe deformation do not approach those appearing during continuous change at a constant strain rate. The nature of such strain-induced events is irreversible and athermal. The mechanisms of continuous dynamic recrystallization operating during severe deformation are discussed in detail.