Effect of current density on the microstructure, corrosion behaviour of plasma electrolytic oxidation treated AM50 magnesium alloy

Abstract

Plasma electrolytic oxidation (PEO) of an AM50 magnesium alloy was accomplished in a silicate based electrolyte using a DC power source. Coatings were produced at three current densities i.e. 15 mAcm-2, 75 mAcm-2, 150 mAcm-2 and were characterised for thickness, roughness, microstructural morphology, phase composition, and corrosion resistance. Even though the 15 minutes treated coatings produced at higher current density levels were thicker, they showed poor corrosion resistance when compared to that of the coatings obtained at 15 mAcm-2. Short term treatments (2 minutes and 5 minutes) at 150 mAcm-2 yielded coatings of thickness and corrosion resistance comparable to that of the low current density coatings. The superior corrosion resistance of the low thickness coatings is attributed to the better pore morphology and compactness of the layer.