Corrosion resistance, composition and structure of RE chemical conversion coating on magnesium alloy

Golden yellow rare earths chemical conversion coating was obtained on the surface of magnesium alloy by immersing in cerium sulfate solution. The corrosion resistance of RE conversion coating was evaluated using immersion test and potentiodynamic polarization measurements in 3.5% NaCl solution. The morphologies of samples before corrosion and after corrosion were observed by SEM. The structures and compositions of the RE conversion coating were studied by means of XPS, XRD and IR. The results show that, the conversion coating consists of mainly two kinds of element Ce and O, the valences of cerium are +3 and +4, and OH− exists in the coating. The anti-corrosion property of magnesium alloy is increased obviously by rare earths conversion coating, Its self-corrosion current density decreases and the coating has self-repairing capability in the corrosion process in 3.5% NaCl solution.