Micro-are oxidation (NMO) coatings were prepared on a SiCp/A356 composite. The microstructure and phase composition of the coatings on the SiCp/A356 composite were examined by XRD and SEM methods. It was found that there were two layers in the coating, a dense layer which was mainly composed of crystalline alpha-Al2O3 and a loose layer which consisted of gamma-Al2O3 and mullite. The coating was well bonded to the SiCp/A356 substrate. The corrosion behavior of the coated and uncoated SiCp/A356 composites was evaluated with a salt spray test and a potentiodynamic polarization technique. The results of the salt spray test showed that the coating could improve the corrosion resistance of SiCp/A356 by 11 times. The corrosion potential was shifted significantly in the anodic direction and the corrosion current density of the coated SiCp/A356 composite was reduced.

Keywords: aluminum matrix composites; micro-arc oxidation; ceramic coating; corrosion