Photocatalytic performance of magnesium alloy microarc oxides

Abstract

Microarc oxidation (MAO) coatings were prepared on AZ91D magnesium alloy in a phosphate electrolyte with and without K2TiF6, respectively. The morphology, composition and phase structure of the MAO coatings were investigated. Corrosion resistances and photocatalytic properties of the MAO coatings were evaluated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) in 3.5wt.% NaCl solution and photocatalytic decomposition of methylthionine blue (MB) solution in incandescent light. Gray coatings formed in the phosphate electrolyte were mainly composed of MgO and amorphous phase. Compared with the phosphate electrolyte, black coatings with fewer and smaller micropores were formed in the electrolyte with K2TiF6. Moreover, Titanium in the form of Mg2TiO4 and TiO2 was detected in the black coatings. The results of corrosion tests show that the MAO coatings formed in the phosphate electrolyte with and without K2TiF6 both improved significantly the corrosion resistance of the magnesium alloy. Photocatalytic measurements indicated that the MAO coatings formed in the electrolyte with K2TiF6 exhibited photocatalytic behaviors.