Abstract:The microstructural evolution and phase transformations during partial remelting of in-situ Mg₂Si_p/AM60B composite modified by SiC and Sr were investigated. The results indicate that SiC and Sr are effective for refining primary α-Mg grains and Mg₂Si particles. After being partially remelted, a semisolid microstructure with small and spheroidal primary α-Mg particles can be obtained. The microstructural evolution during partial remelting can be divided into four stages:the initial rapid coarsening, structural separation, spheroidization and final coarsening, which are essentially caused by the phase transformations of β→α, α+β→L and α→L, α→L, and α→L and L→α, respectively. The Mg₂Si particles have not obvious effect on the general microstructural evolution steps, but can slower the evolution progress and change the coarsening mechanism. During partial remelting, Mg₂Si particles first become blunt and then become spheroidal because of melting of their edges and corners, and finally are coarsened owing to Ostwald ripening.

Key words: magnesium alloy; partial remelting; thixoforming; microstructure evolution; phase transformation; in-situ composite