Isochronal annealing behavior of magnesium alloy AZ31 after hot deformation

Annealing behaviors of hot-deformed magnesium alloy AZ31 were studied at temperatures of 373 to 673 K by optical and SEM/EBSD metallographic observation. The hot-deformed alloy had fine-grained structures developed by grain fragmentation due to continuous dynamic recrystallization (cDRX). Temperature dependence of the average grain size (D) is categorized into three temperature regions, i.e. (a) an incubation period for grain growth at < 450 K, (b) rapid grain coarsening at 473-523 K, and (c) normal grain growth at T > 550 K. The number of fine grains per unit area, however, is reduced remarkably even in region (a). These lead to grain coarsening taking place continuously in the whole temperature regions. In contrast, the deformation texture scarcely changes even after full annealing at high temperatures. It is concluded that the annealing processes operating in hot-deformed magnesium alloy with cDRXed grain structures can be mainly controlled by grain coarsening accompanied with no texture change, that is continuous static recrystallization (cSRX).