Grain Refinement Mechanisms in Gradient Nanostructured AZ31B Mg Alloy Prepared via Rotary Swaging

Gradient nanostructured AZ31B Mg alloy rods were prepared via cold rotary swaging in this study. The swaged sample exhibited the best strength-elongation combination published for the AZ31B Mg alloy. Grain refinement mechanisms during deformation were explored using transmission electron microscopy. The results show that in the initial stage high-density deformation twins first divided the coarse grains into a fine lamellar structure; subsequently, massive dislocation arrays further refined the twin lamellae into finer subgrains; finally, randomly oriented nanograins formed via dynamic recrystallization caused by both deformation heat and increased stored energy. The gradient microstructure along the radial direction was mainly formed by different loading modes. The grains at the center were subjected to loading almost equally from all radial directions, while those at the edge experienced loading only from one direction.