Microstructural evolution and phase transformations during partial remelting of AZ91D magnesium alloy refined by SiC

Abstract

The microstructural evolution and phase transformations have been investigated during partial remelting of AZ91D magnesium alloy refined by SiC particles. Simultaneously, the effect of heating temperature on semisolid microstructure has also been discussed. The results indicate that a semisolid microstructure with small and spheroidal particles can be obtained after the AZ91D alloy being partially remelted. The microstructural evolution can be divided into four stages, the initial coarsening, structural separation, spheroidization and final coarsening, which are attributed to the phase transformations of β → α, α + β → L and α → L, α → L, and α → L and L → α, respectively. Proper rising heating temperature is beneficial for achieving good semisolid microstructure available for thixoforming. For most of the primary particles in the semisolid microstructure, one particle originates from one original dendrite in the as-cast microstructure.