Micro Arc Oxidation Coatings on AZ31B Magnesium Alloy with Different Voltages: Microstructure, Tribocorrosion and Electrochemical Properties

Micro arc oxidation (MAO) played a positive role in surface modification treatment of magnesium alloys (MAs), and their hardness was further improved, which could be applied in aerospace, automotive industry and biomedical fields. In this study, oxide coatings were form on AZ31B MA using MAO with the different voltages. The influence of voltage on the microstructure, tribocorrosion and electrochemical properties of obtained coatings was investigated, and the wear and corrosion mechanisms were also discussed in detail. The results show that the MAO coatings are composed of MgO and Mg₂SiO₄ phases, and their thicknesses, surface roughness and nanohardness are increased with the voltage, which are depended on the reactions of MAO. The average COFs and wear rates of MAO coatings are decreased with the voltage, presenting the superior friction reduction and wear resistance. The wear mechanism of MAO coatings is abrasive wear and oxidative wear, which is attributed to the increase of hardness by the MAO process. The corrosion current density of MAO coating fabricated at 410 V is lower 1 to 2 orders than those of other MAO coatings, showing the best corrosion resistance. Moreover, the R_ct of MAO coating fabricated at 410 V is the maximum, and its N_A is the minimum, showing the best corrosion resistance.