Microstructure evolution of SiC_p/ZM6 (Mg-Nd-Zn) magnesium matrix composite in the semi-solid state

The first reported microstructural study of Mg-RE alloy matrix composites in the semi-solid state was presented. Mg-Nd-Zn (ZM6) alloy matrix composites reinforced with SiC particles were fabricated by mechanical stir casting and extrusion. Semi-solid slugs of SiC_p/ZM6 composites were prepared by semi-solid thermal transformation (SSTT) route and recrystallization and partial melting (RAP) route, respectively. The microstructure evolution of as-cast and as-extruded SiC_p/ZM6 composites during semi-solid remelting was examined under the same conditions. The coarsening mechanisms of SSTT and RAP composites were discussed. The results show that the microstructures of RAP SiC_p/ZM6 composites consist of fine and spheroidal solid grains surrounded by intergranular liquid, while the SSTT composites consist of inferior microstructures with coarse solid grains and high proportion of intragranular liquid droplets. The solid grain coarsening during partial remelting is dominated by coalescence and Ostwald ripening for SSTT and RAP SiC_p/ZM60 composites, respectively. The formation of intragranular liquid droplets and entrapped SiC particles were also discussed.