The effect of Sb ₂ O ₃ on the properties of micro‐arc oxidation coatings on magnesium alloys

Abstract Coatings incorporated with Sb ₂ O ₃ were obtained on AZ31B magnesium alloy during micro‐arc oxidation (MAO) by adding Sb ₂ O ₃ (0, 2, 4, 6, 8 g/L) into the electrolyte. The voltage of MAO process, microstructure, element distribution, thickness, phase analysis, microhardness, adhesion, and corrosion behavior of the coatings were, respectively, investigated. The results showed that the addition of different concentrations of Sb ₂ O ₃ caused the voltage variation, which resulted in the changes in microstructure, element distribution, and phase composition of coatings, and further led to the improvement of coatings properties. It was found that the addition of Sb ₂ O ₃ could effectively decrease the breakdown voltage, and made the voltage of micro‐arc oxidation stage change. Moreover, the presence of Sb ₂ O ₃ influenced surface morphologies of the coatings. Additionally, with the increase in Sb ₂ O ₃ , the microhardness of coatings was 155.2, 199.78, 277.34, 267.53, and 127.93 HV, respectively; these were higher than substrate (68.5 HV). Moreover, the addition of Sb ₂ O ₃ effectively improved adhesion. As the Sb ₂ O ₃ increased, the corrosion rate was 2.19 × 10 ⁻⁴ , 9.09 × 10 ⁻⁵ , 4.10 × 10 ⁻⁵ , 2.52 × 10 ⁻⁴ , and 2.96 × 10 ⁻⁴ mm/a, respectively, and the corrosion resistance increased first and then decreased with the increase in Sb ₂ O ₃ . In sum, the optimal Sb ₂ O ₃ concentration was 4 g/L.