Effect of ammonium metavanadate on surface characteristics of oxide layer formed on Mg alloy via plasma electrolytic oxidation

This study examined the surface characteristics of oxide layers formed on Mg alloy sample by plasma electrolytic oxidation (PEO) coating in phosphate electrolytes with and without ammonium metavanadate (NH4VO3). Depending on the addition of NH4VO3 to the electrolyte, the voltage behavior changed significantly with increasing coating time. This was attributed mainly to the different electrochemical reactions, which might cause the formation of V2O3 and V2O5 in the oxide layer. After the PEO coating for 200 s, the size and number of micro pores decreased with the addition of NH4VO3 to the electrolyte. In addition, the surface color of the sample coated in the NH4VO3-containing electrolyte appeared dark due to the successful incorporation of vanadium oxides. The potentiodynamic polarization test in the 3.5 wt.% NaCl solution showed that the sample PEO-treated in the electrolyte with NH4VO3 had better corrosion-protection properties than that treated without NH4VO3.