Competitive twinning behavior in magnesium and its impact on recrystallization and texture formation

Rolled pure Mg and Mg-1 wt% Gd alloy were subjected to room temperature in-plane compression along the rolling direction, followed by isochronal annealing treatments for 1 h. The results of deformation texture and microstructure showed substantial differences due to rare earth alloying. In spite of imposed c-axis extension during deformation, the Mg-1Gd alloy retained the initial texture with the majority of basal poles concentrated near the longitudinal direction of the used channel-die tool. Electron back scatter diffraction analysis of the deformation microstructure revealed a predominance of {101̅1} compression and {101̅1}-{101̅2} double twins relative to coexisting {101̅2} tension twins. This behavior was significantly contrasting in comparison with that of pure Mg, wherein first and second generation {101̅2} tension twins were observed in profuse quantities. Continuous dynamic recrystallization took place inside compression and double twins by means of slip assisted subgrain rotation about the [0001] axis giving rise to a sharp prismatic fiber of recrystallized orientations. This fiber was transformed into a randomized texture pattern during subsequent static recrystallization and grain growth due to a different discontinuous recrystallization mechanism. This resulted in a significant annealing texture weakening and an increase of the overall Schmid factor for basal slip.