Improving the Semisolid Deformation Behavior and Thixoformability of AZ61 Magnesium Alloy Through Controlling the Strain Induced Melt Activation Process

The present work deals with the microstructure globularization, coarsening behavior and the correlated kinetics during strain-induced melt activation process of AZ61 magnesium alloy. In this study, the effect of pre-strain, temperature and holding time have been considered, and the evolutions were numerically discussed based on Lifshitz-Slyozov-Wagner (LSW) and Ostwald ripening mechanisms. The treated microstructures (undeformed, globular, non-globular, and coarsened) were then hot compressed at a semisolid temperature range to assess the thixotropic flow behavior of the material. A unique microstructure encompassing fine α-Mg globules uniformly distributed in the matrix and surrounded by a liquid phase was developed by imposing 45% pre-strain and holding it at 555°C for 8 min. The lowest deformation resistance belonged to the specimens holding globular microstructures, while those with undeformed characteristics possessed the highest flow stress during thixoforming. The semisolid flow response was discussed considering the flow of liquid that incorporates solid particles (FLS); sliding between solid particles (SS), and plastic deformation of solid particles (PDS) mechanisms. The influence of the shape factor (in globular structure) and the grain size (in coarsened structure) on the thixotropic flow behavior of the experimented alloy were also illustrated.