Strain induced transformation, dynamic recrystallization and texture evolution during hot compression of an extruded Mg-Gd-Y-Zn-Zr alloy

The recrystallization mechanism and texture evolution of Mg-8.3Gd-3.6Y-1.6Zn-0.5Zr (wt. %) alloy were investigated in the course of thermomechanical processing at the temperature range of 300-500 degrees C. The correlation with high temperature flow behavior and the subsequent room temperature mechanical properties have been also assessed. The results indicated that the workability of the alloy was significantly improved owing to the occurrence of continuous dynamic recrystallization, where the recrystallized grain size decreased down to similar to 3 and similar to 1 mu m at temperatures of 350 and 400 degrees C, respectively. In addition, the volume fraction of blocky long period stacking ordered (LPSO) phases was increased dynamically at 350 and 400 degrees C. The presence of blocky LPSO phases in high volumes acted as the particle stimulated nucleation (PSN) mechanism. At temperature of 500 degrees C, some of the blocky LPSO phases dissolved in the matrix, and this in turn could lead to the precipitation of lamellar ones in the recrystallized grains. Decrease in the basal slip Schmid factor due to the formation of blocky and lamellar LPSOs in the area inside the grains containing these phases demonstrates the important role of these phases in the hardening which is in competition with softening due to dynamic recrystallization. The corresponding texture analysis indicated that recrystallization through PSN could decrease the basal intensity thereby inducing a significant texture weakening effect. Interestingly, an appreciable enhancement in the stretch formability properties was achieved, which were justified considering the effect of grain size, volume fraction of both blocky and lamellar LPSO phases and texture.