Refinement of recrystallized grains of AZ31 magnesium alloy sheets by asymmetric rolling

Abstract

For the purpose of grain refinement of AZ31 magnesium alloy sheets, influences of asymmetric rolling conditions such as the roll temperature and the mismatch speed ratio on microstructures and texture were examined, and compared with those of conventional rolling sheet. Grain size of the annealed sheets processed at a roll temperature of 80°C and the rolled sheets processed at a roll temperature of 250°C decreases with increasing mismatch speed ratio. And at a mismatch speed ratio of 1.5, the grain size of 4.2 and 2.4 μm are obtained in the former and the latter, respectively. There is not an obvious difference in textures between the conventionally rolled and the asymmetrically rolled sheets. Proof stresses on the sheets annealed after rolling at 80°C and on the sheets rolled at 250°C increased with decreasing the grain size. Hall-Petch plot for both the sheets showed a good linearity expressed with σ0.2% =95+0.20d-1/2. The grain refinement by asymmetric rolling at a roll temperature of 250°C seems to result from the promotion of a continuous recrystallization by a simultaneous action of two deformation mode, namely compression and additional shear deformation.