Oxidation coatings were prepared on the surface of AZ31B magnesium alloy by micro-arc oxidation in the electrolytes with CoSO 4 addition varying from 0 to 0.8 g/L. The effects of different concentrations of CoSO 4 on the properties and microstructure of the coating were analysed by Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Xray Diffraction (XRD) and Electrochemical Workstation. The results revealed that the addition of different concentrations of CoSO 4 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 CoSO 4 addition, the morphology of the coating was changed. XRD patterns and XPS confirmed that Co 3 O 4 , MgO and Mg 2 SiO 4 were generated. The addition of CoSO 4 could effectively improve the hardness, corrosion resistance and thermal-shock resistance.

MgO micro-powder of different concentrations from 0 to 8 g L −1 was added in the electrolyte. Effects of MgO micro-powder concentration on properties of micro-arc oxidation (MAO) coating were analysed by scanning electron microscopy, energy dispersive spectrometer, X-ray diffraction, electrochemical workstation, thermal shock tester equipment, etc. The result revealed that the concentration of MgO has evident effects on the properties of the MAO coating. When MgO micro-powder increased, the oxide voltage, the coating thickness and hardness increased first and then decreased. In this case, the diameter of the hole on the coating surface also increased and more linear holes appeared. The phases mainly consist of γ-Al 2 O 3 , α-Al 2 O 3 , MgAl 2 O 4 and Mg 2 SiO 4 . As a result, the corrosion resistance and the adhesion of the MAO coating increase first and then decrease mainly related to the surface morphologies and phase of the coating. The coating has good thermal shock resistance. The performance of micro-arc oxidation coating with MgO micro-powder was improved.

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Micro-arc oxidation coatings were fabricated on 7E04 aluminum alloy substrates by micro-arc oxidation (MAO) in the electrolytes with the graphite addition varying from 0 to 8[Formula: see text]g/L (0, 2, 4, 6, 8[Formula: see text]g/L). The effect of graphite concentration on the surface morphologies, micro-hardness, thickness, phase composition and corrosion resistance of coatings was investigated. With the graphite powder concentration increasing, the oxidation voltage decreased gradually and the thickness of coatings firstly dropped down and then went up. It is found that the size of micro-pores and sintered discs declined with increase of graphite concentration. The XRD results indicated that MAO coatings mainly consisted of [Formula: see text]-Al2O3, [Formula: see text]-Al2O3, SiO2 and a little [Formula: see text]-Al2O3. The corrosion resistance of coatings was improved with the addition of graphite powder. The study reveals that the appropriate graphite powder in the electrolytes is essential to promote the performance of the coatings.