Underlying mechanisms of variation in yield asymmetry and strain hardening behavior of extruded pure Mg with Gd addition

Effects of Gd addition on the strain hardening behavior and yield asymmetry of pure Mg are investigated by subjecting extruded pure Mg, Mg–5Gd, and Mg–15Gd (all in wt%) to tension and compression tests along the extrusion direction (ED). As the amount of Gd added to pure Mg increases, the basal texture tilts toward the ED and the distribution of c-axes of grains becomes randomized. Under tension, the strain hardening rates of all the materials decrease until fracture. However, under compression, the strain hardening rate increases in the early stage of deformation in pure Mg and Mg–5Gd, whereas it continuously decreases in Mg–15Gd. Pure Mg exhibits considerably high tension-compression yield asymmetry, with a compressive yield strength (CYS) to tensile yield strength (TYS) ratio of 0.4. In contrast, Mg–5Gd exhibits excellent yield symmetry with CYS/TYS of 0.9 and Mg–15Gd exhibits reversed yield asymmetry with CYS/TYS of 1.2. Underlying mechanisms of these drastically different Gd-addition-induced deformation behaviors of the materials are discussed in terms of the crystallographic distribution of grains and the relative activation stresses of basal slip, prismatic slip, pyramidal slip, and {10–12} twinning under tension and compression.