The hydrothermal performance and corrosion resistance of MgO@Nb2O5 composite coatings on Mg–7Y alloy in natural seawater

MgO@Nb2O5 composite coating was prepared on the surface of Mg–7Y alloy by micro-arc oxidation technique. The microstructure of the composite coatings was tested by scanning electron microscopy, energy spectrum analysis, X-ray diffraction and scanning kelvin probe force microscope. The hydrothermal performance and corrosion resistance of MgO@Nb2O5 composite coatings were analyzed by electrochemistry tests and laser confocal. The results showed that microspore diameter, porosity and roughness of the composite coatings were all decreased with the increasing of Nb2O5 concentration. The micro-arc oxidation composite coatings were mainly composed of MgO and Nb2O5. Compared with the micro-arc oxidation coating without Nb2O5, the corrosion voltage of the micro-arc oxidation coating with Nb2O5 was increased and the corrosion current was reduced. The corrosion resistance of Mg–7Y alloy was effectively improved by the MgO@Nb2O5 composite coatings, and the best corrosion resistance of the micro-arc oxidation coating was achieved when the Nb2O5 concentration was 2 g/L. The hydrothermal test demonstrated that the hydrothermal resistance of the coatings was significantly improved due to the addition of Nb2O5.