Microstructure stability of cold drawn AZ31 magnesium alloy during annealing process

The microstructural evolution of heavily cold drawn AZ31 magnesium alloy wires was investigated during a wide range of annealing temperature from 200 to 450°C. The results show that the mean grain size of the as-annealed material is sensitive to the annealing temperature and cold drawn area reduction. Upon annealing symmetrical grain growth takes place in the AZ31 wires of cold drawn area reduction 12.2% under all the investigated annealing conditions, while three different stages of grain size refinement, normal grain growth and abnormal grain coarsening occur gradually in the materials with cold drawn area reduction 23.0%–60.5% with annealing temperature increasing. The increase of cold drawn reduction leads to the decrease of critical annealing temperatures for the three periods, and also enhances the start of abnormal growing grains preferentially in the severely drawn materials from the outer surface where larger amount of shear deformation constitutes the driving force for growth.