The role of low-angle grain boundaries in multi-temperature equal channel angular pressing of Mg–3Al–1Zn alloy

Equal channel angular pressing was used to process an AZ31B magnesium alloy (nominally Mg–3Al–1Zn in wt%) at temperatures decreasing from 200 to 150 °C. The resulting microstructure was characterized by electron backscattered diffraction to reveal the role of low-angle grain boundaries in grain refinement. It was found that low-angle grain boundaries with misorientation angles lower than 5° are surrounded by regions of increased strain gradients, which can stimulate the generation of non-basal slip dislocations during the equal channel angular pressing at temperatures of approximately 150 °C. The strain gradients in the vicinity of the grain boundaries with misorientation angles in the range of 5°–10° were less frequent or were completely absent for high-angle grain boundaries with misorientation angles higher than 10°. This article also discusses the importance of low-angle grain boundaries for the generation of non-basal 〈c+a〉 dislocations needed for successful equal channel angular pressing of AZ31B at temperature of 150 °C.