Microstructure evolution of semi-solid Mg–10Gd–3Y–0.5Zr alloy during isothermal heat treatment

In this study, the microstructure evolution of semi-solid Mg–10Gd–3Y–0.5Zr alloy during isothermal heat treatment has been investigated. The results show that primary particles coarsen continuously during the holding. Coarsening rate decreases with the increase of isothermal temperature. When isothermal temperature increases from 600 °C to 620 °C, the dominant mechanism for coarsening changes from particle coalescence to Ostwald ripening. Equiaxed as-cast microstructure is beneficial to the semi-solid microstructure after isothermal heat treatment, which brings about the refinement and spheroidization of primary particles, and shortening of holding time. Significant modification of second phases can also be achieved after isothermal heat treatment, due to its unique solidification process. The optimum processing parameters for Mg–10Gd–3Y–0.5Zr alloy in isothermal heat treatment are isothermal temperature of 610 °C–620 °C and holding time of 20–40 min.