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In this research, magnesium oxide/hydroxyapatite/graphitic carbon nitride composite coatings were prepared using electrolyte containing particles of hydroxyapatite and graphite carbon nitride on magnesium AZ31 alloy by micro-arc oxidation (MAO) method in order to expand the application of this alloy in industries such as aerospace and medicine. The effect of the hydroxyapatite and graphitic carbon nitride concentration on the microstructure, composition and corrosion properties of the coating was investigated. The results of the microstructure study and elemental analysis through field emission scanning electron microscopy (FESEM) and Energy Dispersive Spectroscopy (EDS) confirmed that hydroxyapatite and graphitic carbon nitride are well in the coating structure with porous morphology (outer porous layer, inner compact layer) have been absorbed and were mostly placed in the inner compact layer. By increasing the concentration of graphite carbon nitride, more particles were included in the coating and the corrosion resistance of the uncoated sample increased from 119.5 Ω.cm2 to 1896 Ω.cm2. The evaluation of the electrochemical behavior of the samples using the potentiodynamic polarization test showed that the sample with 5 g/L graphitic carbon nitride and 10 g/L hydroxyapatite has the best corrosion performance among the samples and its polarization resistance is 5 times that of the uncoated sample. Investigating the corrosion process using Electrochemical Impedance Spectroscopy (EIS) showed that the compactness of the coating and the difficulty of penetrating the corrosive ions into the inner layer is related to the presence of graphite carbon nitride particles in the inner layer of the coating.

Keywords: Micro arc oxidation, AZ31 magnesium alloy, hydroxyapatite, graphitic carbon nitride, corrosion

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