Microstructure and heterogeneous nucleation phenomena in cast SiC particles reinforced magnesium composite

The microstructure and heterogeneous nucleation phenomena in cast SiC particles reinforced magnesium composite have been studied using optical and transmission electron microscopy (TEM). The microstructure of magnesium composites showed that most SiC particles were pushed and segregated at the grain boundaries while few SiC particles (3%) were entrapped in the magnesium grain. The SiC particles in the magnesium composite were identified as 6Hα-SiC structure. Stacking faults and pits defects were also observed within the SiC particles. The primary magnesium phase which heterogeneously nucleated on the SiC particle surface has been identified with a small lattice disregistry (2.3%) while their crystallographic orientation relationship was (101̄0)Mg//(0001)SiC. Examination of the composite interface indicated that the eutectic and Cu5Zn8 phases were able to wet the SiC particles and heterogeneously nucleate on the SiC particles while the crystallographic orientation relationships between them were (011̄1)SiC//(110)Mg17Al12 and (0001)SiC//(001)Cu5Zn8, respectively. Finally, the factors that influence the heterogeneous nucleation of primary magnesium phase, eutectic and Cu5Zn8 phases on the SiC particles are discussed.