Correlation of static recrystallization and texture weakening of AZ31 magnesium alloy sheets subjected to high speed rolling

MagnesiumAZ31alloy sheets were rolled at a high speed of 1000 m/min(HSR) and a low speed of 15 m/min(LSR) at 100 °C to a reduction of 30%. The as-rolled microstructures were heavily twinned and shear banded at both speeds. Annealing was performed on the as-rolled sheets at three different temperatures (200, 350 and 500 °C) for increasing time intervals. Texture weakening was achieved after annealing of both HSRed and LSRed sheets due to static recrystallization (SRX) on twins and shear bands. This, in turn, greatly improved the ductility of the sheets. It was found that the intensities of the basal texture of the HSRed specimens were lower than those of the LSRed specimens at as-rolled and all annealed conditions. This is related to the higher amount of contraction twins and more slips activated during HSR. Correlation of the maximum intensity of the basal texture with softening/recrystallization fraction was found to be involved in two weakening stages. During the first stage, nucleation on twins and shear bands was the dominant mechanism for texture weakening, while growth of the non-basal grains was responsible for the second stage of texture weakening. Interestingly, it was found that the weakest texture was attained after annealing at 500 °C for 5 min in the HSRed specimen, which can be related to thermal activation of more random nucleation sites and preferential grain growth of the non-basal oriented grains.