Influence of silicon on growth process of plasma electrolytic oxidation coating on Al–Si alloy

Ceramic coating was formed on the surface of Al–Si alloy via plasma electrolytic oxidation (PEO) technique. The influence of silicon on the growth process, morphology and composition of the PEO coating was investigated. It was observed that the coating was simultaneously formed on the surface of primary α phase and eutectic (α + β) in the initial stage of PEO process. No plasma discharge occurred on the surface of eutectic Si phase. But the silicon would be oxidized and mixed with Al2O3 in coating melted at high temperature. The PEO coating on primary α phase was mainly composed of Al2O3. By contrast, the content of SiO2 in coating formed on eutectic (α + β) was higher than that of Al2O3. With the time increasing, the amount of α-Al2O3 in the PEO coating increased because of the transformation from γ-Al2O3 to α-Al2O3 at high temperature.