Interfacial microstructure evolution in aluminium matrix composites reinforced with unoxidized and oxidized SiC particles

Interfacial microstructure evolution of Al matrix composites with non-oxidized and oxidized SiC particles as reinforcement was investigated using x-ray diffraction, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Hexagonal platelet-shaped Al₄C₃ and Si are the two major interfacial reaction products in the non-oxidized SiC-particle-reinforced Al matrix composites (SiCp/Al). In addition, the eutectic θ-CuAl₂ and Si phases precipitate at the SiCp/matrix interface during the last solidification stage. Observation of the interfacial reaction between the oxidized SiC particles and Al alloy containing Mg shows that the SiO₂ layer has good bonding with both SiC and Al matrix and that nanoparticles of MgO have formed initially. The MgO particles will change into octahedral MgAl₂O₄ crystals when there is a low Mg content in the matrix (≤2 wt.%) and will remain as MgO when there is a high Mg content (≥4 wt.%).