Rare earth conversion coating on Mg–8.5Li alloys

The conversion coating formed by immersion in a solution containing rare earth salt on Mg–8.5Li alloy was studied and the corrosion resistance was evaluated as well. The surface morphology was observed by scanning electron microscopy (SEM), and the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). The corrosion behaviors of Mg–8.5Li alloy and conversion coating were assessed by means of potentiodynamic polarization curves, electrochemical impedance spectra (EIS) and immersion tests. The experimental results indicated that the coating with cracked morphology was homogeneous. It was mainly composed of La2O3, CeO2, Mn2O3 and MnO2 as detected by XPS. The results of electrochemical measurements and immersion tests revealed that the rare earth conversion coating possessed better corrosion resistance than bare alloy and chromate conversion coating.