Microstructure and mechanical properties of AZ31 magnesium alloy sheets produced by differential speed rolling

The as-extruded AZ31 alloy sheets of 10 mm in thickness were subjected to differential speed rolling (DSR) process performed on a mill, of which the rotation speed ratio of the lower roll and upper one is kept at constant 1.05 by using the different upper and lower roller diameters. The influence of the billet temperature, pass and total thickness reduction ratio on the microstructures, mechanical properties and crystal orientation of the specimens were examined by optical microscopy, tensile test and X-ray diffraction. The present process was found to be effective to refine the grain size and restrain the twinning. Grain refinement became more marked and uniform when the pass and total thickness reduction ratio increased, and the sheets processed by DSR exhibited higher elongation and lower strength than those of the conventional rolled sheets under the same testing conditions. Especially, the AZ31 sheet with elongation of 32% at room temperature was prepared. Moreover, anisotropy was diminished by further annealing at 573 K for 30 min. The DSR does not alter the basal texture but leads to the incline of the basal plane from the sheet surface plane to some extent.