Microstructural evolution of predeformed SiCp/ZA27 composites during partial remelting

The microstructural evolution process in SiC particle (SiCp)-reinforced ZA27 composites, previously compressed by different lengths at 270 degreesC, was investigated during partial remelting. The results indicated that, after being compressed, the microstructure of SiCp/ZA27 composites changed gradually from developed primary alpha 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 a particle size with the heating time obeyed the law developed by Lifshitz and Slyosov and Wagner (LSW) after the semisolid system was up to the dynamic solid-liquid equilibrium state. High compression, high remelting temperature, and large size and proper content of SiC(p)s were beneficial to achieving a desirable structure for semisolid forming (SSF). The primary a particle size distribution was significantly affected by coalescence. These phenomena were extensively discussed metallographically and theoretically.