Primary recrystallization of a magnesium hybrid material fabricated by high-pressure torsion

The static recrystallization and grain growth of a hybrid AZ31/Mg-0.6Gd (wt%) material fabricated by high-pressure torsion (HPT) through 20 turns were explored after isochronal annealing at 150, 250, 350 and 450 degrees C for 1 h using electron backscatter diffraction, transmission electron microscopy and Vickers microhardness measurements. The results reveal heterogeneity in the grain size distributions of the AZ31 and Mg-0.6Gd regions after annealing at the lower temperatures of 150 and 250 degrees C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 degrees C the AZ31/Mg-0.6Gd interfaces were not well-defined owing to the occurrence of grain growth. It is shown that grain growth is restricted in the AZ31 and Mg-0.6Gd regions due to the presence of stable nano-size Al8Mn5 particles and the precipitation of Mg17Al12 and Mg12Zn at 250 degrees C and of Mg5Gd and Mg12Gd phases at 350 and 450 degrees C. The distribution of the basal texture in both regions was strongly controlled by dynamic recrystallization, precipitation and grain growth. The values of the microhardness over the radial cross-sections of the hybrid discs decrease and become more uniform, in the range of similar to 35-66 Hv, with increasing annealing temperature.