Dislocation-driven recrystallization in AZ31B magnesium alloy imaged by quasi-in situ EBSD in annealing experiments

Abstract

We led a series of annealing experiments with quasi-in situ electron backscattered diffraction (EBSD) measurements to characterize the effect of the deformation microstructure on static recrystallization. Six samples of commercial purity AZ31B magnesium alloy were deformed under different temperature and strain rate conditions to produce microstructures with variable dislocation densities and arrangements, and then heated at 300 °C (0.64 Tm) for up to 6 h in several steps. All samples recrystallized by the growth of substructure-free grains, with nuclei mainly inherited from the deformed state. Recrystallization proceeded rapidly (minutes to hours), but remained incomplete in all cases. Using textural and microstructural proxies, we show that, under the studied experimental conditions, the stored energy associated with the dislocations controls the recrystallization kinetics. We observe a positive correlation between the initial average kernel average misorientation (KAM) and the recrystallization kinetics of each sample and, to a lesser extent, the recrystallized fraction at a given time. We also present direct evidence on how the stored energy in the vicinity of the recrystallization front controls grain boundary migration kinetics. Yet, the reduction in the stored energy alone cannot explain the stagnation of the recrystallization front and incomplete recrystallization.