Effect of CoSO 4 on the characteristics of micro-arc oxidation coatings

Abstract

Oxidation coatings were prepared on the surface of AZ31B magnesium alloy by micro-arc oxidation in the electrolytes with CoSO₄ addition varying from 0 to 0.8 g/L. The effects of different concentrations of CoSO₄ on the properties and microstructure of the coating were analysed by Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD) and Electrochemical Workstation. The results revealed that the addition of different concentrations of CoSO₄ caused the voltage variation, which resulted in the changes of microstructure, phase composition and element distribution of coatings. Furthermore, it led to the improvement of coating properties. It was found that the oxidation voltage increased firstly and then decreased. Because of CoSO₄ addition, the morphology of the coating was changed. XRD patterns and XPS confirmed that Co₃O₄, MgO and Mg₂SiO₄ were generated. The addition of CoSO₄ could effectively improve the hardness, corrosion resistance and thermal-shock resistance.