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

Abstract

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 °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 °C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 °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 °C and of Mg5Gd and Mg12Gd phases at 350 and 450 °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 ~35–66 Hv, with increasing annealing temperature.