Carbon fibre-reinforced aluminium composites were pressurelessly cast by using K2ZrF6 as the wetting promotion agent. Transmission electron microscopy (TEM) and energy dispersed analysis of X-rays, (EDAX) were used. The results showed that interfacial reactions were very active after K2ZrF6 treatment. This was caused by the diffusion and reaction of zirconium in the surface of carbon fibres or in the SiC coating. Silicon alloying of aluminium could suppress the interfacial reactions by decreasing the activity of zirconium and changing intermetallic Al3Zr to Zr3Al4Si5, and building up the phase equilibrium between SiC, aluminium and silicon. The requested silicon content was higher than the equilibrium content of Al-Si-SiC system to suppress the SiC/Al interfacial reaction. A perfect interface was achieved in SiC-coated carbon fibre Al-12 wt% Si composite.