| Summary: | Effect of V<sub>2</sub>O<sub>5</sub> additive in silicate-containing electrolyte on AZ91D magnesium alloys treated by micro-arc oxidation (MAO) technology under different loading voltages was investigated. The results showed that vanadium was well up-taken into the coating chemically. Moreover, a new phase of MgV<sub>2</sub>O<sub>4</sub> with spinel structure was obtained in MAO coatings due to V<sub>2</sub>O<sub>5</sub> added into the electrolyte. The MgV<sub>2</sub>O<sub>4</sub> phase was responsible for the coatings exhibiting brown color and also was beneficial to improving the anti-corrosion property. In spotting tests, the corrosion resistances of coatings prepared under the high voltage are about 6–9 times higher than those of the low voltage because of the thicker coatings of the former. In potentiodynamic polarization tests, the coatings’ corrosion resistances were improved with the addition of V<sub>2</sub>O<sub>5</sub>, which was more significant under the low voltage than that under the high voltage. When the concentration of V<sub>2</sub>O<sub>5</sub> was 0.2 g/L, the corrosion current density of the coating was the lowest, which means that the coating’s corrosion resistance under the low voltage is the best. Hence, it is necessary to carry out targeted design of the coating’s microstructure according to the different applications.
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