The mechanical and textural response of two strongly textured AZ31B magnesium alloy under free-end torsion

The deformation behavior of two strongly textured AZ31B magnesium alloys was investigated experimentally under free-end torsion loading. Two different initial material orientations are used in the study: one batch of specimens was machined from an extruded bar along the extrusion direction (ED), while the other batch was machined from a rolled plate along the normal direction (ND). The microstructure evolution of the material is examined by means of electron backscattered diffraction (EBSD) using companion specimens. The results show that the ED specimens have higher shear strength and higher elongation than these of ND specimens. The Swift effect was observed in both specimens, but with different characteristics: with no stress applied along the specimen axis during torsion, axial extension and axial contraction are observed on the ED and ND specimens, respectively. In both cases, {10-11} compression twins and {10-11}-{10-12} compression-tension double twins of significant sizes are observed after 32% shear strain, mainly related to the high resolved shear stress on twin variants. With the Schmid factor (SF) of some twin variants reaching the unit, the twin variant selection is mostly Schmid factor-related. The strain accommodation parameter may explain some of the non-SF-related twin variants. The inhomogeneity of the strain is discussed based on the Kernel average misorientation (KAM) maps.