Isothermal semisolid microstructure evolution of compressively deformed AZ91D magnesium alloy billet

The microstructure evolution of AZ91D magnesium alloy semisolid slurry in the SIMA process was investigated, and the influencing factors on spherical microstructure evolution were analyzed. The results show that during the heating stage at 550°C, the morphology of primary α phase changes firstly from dendrites to nubbly crystal, with increasing soaking time it changes gradually from nubbly to polygon and spherical crystal. As soaking time over, combination of grains occurs. With the rising soaking temperature, the grain spheroidization accelerates and the average dimension of grains diminishes at the same soaking time. With the remaining soaking time the grains get rounded, and the increasing deformation rate facilitates the morphology transition of dendrite at the same soaking temperature. The higher the deformation rate is, the faster the dendrite crystal transforms, and the shorter the time spent for the microstructure evolution.