Thermal Stability of an Mg-Nd Alloy Processed by High-Pressure Torsion

The evolution of microstructure, texture, and mechanical properties of an Mg-1.43Nd (wt%) alloy is investigated after processing by high-pressure torsion at room temperature through five turns and isochronal annealing for 1 h at 150, 250, 350, and 450 degrees C using electron backscatter diffraction and Vickers microhardness. The alloy exhibits a good thermal stability up to annealing at 250 degrees C, with mean grain size of approximate to 0.65 mu m. The microhardness shows an initial hardening after annealing at 150 degrees C and then a subsequent softening. The deformation texture, a basal texture shifted 60 degrees away from the shear direction (SD), is retained during annealing up to 250 degrees C. In contrast, a basal texture with symmetrical splitting toward SD is developed after annealing at 350 degrees C. The precipitation sequence and their pinning effects are responsible for the age-hardening, stabilization of grain size, and the texture modification. The kinetics of grain growth in the Mg-1.43Nd alloy follows two stages depending on the temperature annealing range, with an activation energy of approximate to 26 kJ mol(-1) in the low temperature range of 150-250 degrees C and approximate to 147 kJ mol(-1) in the high temperature range of 250-450 degrees C.