Transient plasticity and microstructural evolution of a commercial AZ31 magnesium alloy at elevated temperatures

Mechanical behavior and microstructural evolution during deformation of a commercial AZ31 magnesium alloy with the initial coarse grains and fine grains at elevated temperatures have been studied.; It is found that superplasticity of coarse-grained alloy is lattice diffusion controlled process and can be described by Weertman equation as predicted by Sherby et al. The grain boundary sliding between coarse grains initiated multiple slips including basal and non-basal slip in the grains and finally, due to high temperature, the dislocations climbed to sub-grain boundaries to accommodate the grain boundary sliding. It is found that dislocation slip is the main deformation mechanism. There is a competing mechanism between grain growth and grain refinement during deformation. EBSD studies revealed that the pre-existing weak texture, which is close to (0001) fiber in the as-received Mg plate, evolved into a strong texture close to {lcub}0001{rcub} <11¯00> component. Among the possible slip systems, {lcub}0001{rcub} <11¯20> is the most active slip system, especially in the early stage of deformation. As strain increases it became more and more unfavorable, whereas {lcub}112¯2{rcub} <112¯3¯> became more and more favorable during the process. Slip systems {lcub}11¯00{rcub} <112¯0> and {lcub}11¯01{rcub} <112¯0> kept favored during the whole process of deformation.; For the initially fine-grained alloy, it is found that the deformation is a grain boundary diffusion controlled process even at higher temperatures and with the initial grain size above 15μm, and the main contributions to the large strains come from the grain boundary sliding and non-basal slip. Even with the slightly larger grains compared with the pre-requisite for FFS, significant grain boundary sliding still occurred during deformation, and was even found in the sample deformed to 200% elongation at 773K with the strain rate of 1 × 10−3 s−1, where the mean grain size increased to about 60μm. EBSD studies indicate that the pre-existing strong (0001) fiber texture evolved into a stronger (0001) <11¯00> texture, indicating that slip activities occurred during deformation. Schmid factor analysis indicates that non-basal slips are the most favored slip systems during the whole process of deformation. It is believed that the large strain obtained comes from the grain boundary sliding together with the non-basal slips during deformation.