The effect of pre-existing twin on the shear deformation behavior of AZ31 magnesium alloy

In this research, the shear deformation behavior of an AZ31 magnesium alloy was studied at a temperature range of 200-440 °C by employing shear punch testing method. To introduce twins, a rolled alloy was pre-strained, and the shear deformation of pre-twinned material was compared with the annealed one. The results showed that pre-existing twins led to a higher shear strength owing to the strengthening role of twin boundaries. At 320 °C, due to the activation of nonbasal slip systems, the twin boundaries act as dislocation sink and facilitate dynamic recovery. At high temperatures, as the twins were simply recovered no appreciable difference in deformation behavior and final microstructure could be realized between the alloys with and without twins. Twin boundaries provide more frequent nucleation sites for new grains and also deformation inhomogeneities, increasing the fraction of new grains at 200 and 260 °C. Finer recrystallized grains were obtained during shear deformation, compared to those compression /tension at similar conditions. The latter was discussed relying on the role of shear strain in evolution of fine microstructures.