A STUDY ON THE ORIGIN OF SHEAR BANDS IN COLD ROLLED Mg-3Y ALLOY USING 3D EBSD

In the present study the formation and characteristics of shear bands formed during cold rolling of Mg-3Y (Mg-3 wt. %Y) were investigated using conventional and 3-dimensional EBSD (electron backscatter diffraction)-based orientation microscopy. Shear bands are identified by their low values of diffraction pattern quality. The texture in shear bands is found to reveal the tendency that basal poles are oriented towards the transverse direction (TD) of the sample. Moreover, before initiation of shear bands, the textures of the areas with high strain also exhibit the same tendency as in shear bands. Activation of prismatic slip is proposed to be the reason for this observed TD rotation. Prismatic slip appears to be stimulated by the pile-up and cross slip of basal dislocations at extension twin boundaries. 3D-EBSD was employed to calculate the density of geometrical necessary dislocations (GND). These calculations show that the distribution of <c+a> dislocations is more homogenous than that of <a> dislocations. A number of low-angle grain boundaries mainly caused by <a> dislocations are observed near extension twins before shear banding and near shear bands after the activation of shear bands which further supports the idea that low-angle grain boundaries are involved in shear band formation.