Effects of rare earths on the microarc oxidation of a magnesium alloy

The effects of rare earths on the properties of the microarc oxidation (MAO) coating on a magnesium alloy were investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and electrochemistry methods. The results show that a nice and compact MAO coating was successfully obtained when the magnesium alloy was treated in nitrate solutions as the pre-treatment of MAO. However, the MAO was not successfully completed for the silicate electrolytes with the addition of rare earths. After the magnesium alloy being treated by rare earth nitrate, the obtained MAO coating has advantages such as uniform distribution of thickness, improved corrosion resistance, and nice-uniform surface, as compared with the untreated magnesium alloy. In addition, the time of non-ESP, the voltage and current density of the MAO process obviously decrease. Cerium oxide doped on the surface of the magnesium alloy can significantly improve the corrosion resistance of the MAO coating and decrease the current density of the MAO process, as compared with lanthanum oxide, whereas the doped rare earths have no significant effect on the components of the MAO coating.