Corrosion of Magnesium Alloy AZ31 Coated by Plasma Electrolytic Oxidation

Abstract

In this work, plasma electrolytic oxidation was performed on AZ31 magnesium alloy. The electrolytes contained mixtures of sodium silicate, sodium hexamethaphosphate, potassium hydroxide, and potassium fluoride. Scanning electron microscopy, X-ray diffraction, porosity measurements, atomic analysis, and exposition in 3% NaCl were carried out to investigate the microstructure, elemental/phase composition, and corrosion resistance of the coatings. The results showed that the coating formed in both silicate- and phosphate-containing electrolyte were mainly composed of MgO, Mg(OH)₂, Mg₂SiO₄, and Mg₃(PO₄)₂ showing the most dense structure and the best corrosion resistance.