Improving corrosion resistance of AZ91D magnesium alloy by laser surface melting and micro-arc oxidation

Laser surface melting (LSM) pretreatment and micro-arc oxidation (MAO) were performed to the AZ91D magnesium alloy to improve the corrosion resistance. The microstructure, surface morphologies, phase constituents and electrochemical corrosion behavior were investigated by optical microscope (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) measurements respectively. The results showed that the AZ91D alloy obtained a continuous and uniform laser-melted layer with a thickness of 1 mm and refined microstructure. The MAO coating on laser-melted AZ91D magnesium alloy had refined micro-pores with uniform size than that on the original magnesium substrate without laser melting pretreatment, and correspondingly, the lower corrosion current density and larger MAO coating electrochemical impedance value were found on the AZ91D magnesium alloy with LSM and MAO treatment. It implies that the LSM-MAO coating had more effect on improving the corrosion resistance compared with the singular MAO coating.