Microstructural evolution of predeformed SiC_p/ZA27 composites during partial remelting

The microstructural evolution process in SiC particle (SiC_p -reinforced ZA27 composites, previously compressed by different lengths at 270 °C, was investigated during partial remelting. The results indicated that, after being compressed, the microstructure of SiC_p/ZA27 composites changed gradually from developed primary α dendrites, to coarsened short dendrites, and then to a structure consisting of texture cells with different orientations with increasing compression. During subsequent partial remelting, the microstructure evolution exhibited four stages: initial rapid coarsening, structural separation, spheroidization, and final coarsening. The change of the primary α particle size with the heating time obeyed the law developed by Lifshitz and Slyosov and Wagner (LSW) after the semi-solid system was up to the dynamic solid-liquid equilibrium state. High compression, high remelting temperature, and large size and proper content of SiC_ps were beneficial to achieving a desirable structure for semisolid forming (SSF). The primary α particle size distribution was significantly affected by coalescence. These phenomena were extensively discussed metallographically and theoretically.