Development of decorative and corrosion resistant plasma electrolytic oxidation coatings on AM50 magnesium alloy

Abstract

Plasma electrolytic oxidation of AM50 magnesium alloy was performed in alkaline phosphate electrolyte with and without the addition of titania sol. The coatings produced in the phosphate electrolyte were constituted with MgO and Mg3(PO4)2. The coatings obtained in the phosphate electrolyte with the addition of titania sol were blue in colour and contained additionally the TiO2 and Mg2TiO4 phases. The phosphate PEO coating provided a two order of magnitude improvement in corrosion resistance to the AM50 magnesium alloy as was shown by the potentiodynamic polarisation measurements. With differences in the physical appearance, microstructural morphology and phase composition, the coatings produced in titania sol containing electrolytes offered an improved corrosion resistance compared to the mere phosphate PEO coating.