Isothermal grain coarsening of extruded Mg-5.5Zn-2Gd-0.6Zr magnesium alloy by simple strain-induced melt activation process

The semi-solid microstructure evolution of extruded Mg-5.5Zn-2Gd-0.6Zr experimental magnesium alloy at different isothermal temperatures (600, 610 and 620℃) for different holding time by the simple strain-induced melt activation (SSIMA) process was studied. It is shown that the relationship between the average diameter of α(Mg) grains and the isothermal holding time fits the formula d³- d³₀=K_t at the same isothermal temperature, where the coarsening rate constant K increases with the increase of the isothermal annealing temperature. And its coarsening follows the modified liquid film migration model proposed by Monson-Whitton, et al. α(Mg) grains in longitudinal section coarsen faster than those in transverse section, which is the essential reason of uneven grains in microstructures of the semi-solid slurry prepared by SSIMA process.