Effects of current density on the microstructure and corrosion resistance of MAO coating on extruded AZ80 alloy

Abstract

In this study, microarc oxidation coatings are prepared on the extruded AZ80 magnesium alloy in the silicate electrolyte solution under different current densities. The phase composition and microstructure of the MAO coating are characterized by XRD and SEM, respectively. The MAO coatings are mainly composed of MgO, MgSiO₃ and MgAl₂O₄. Typical porous microstructure can be observed in the coatings. The average diameter of micropores is less than 1 μm. With the current density increasing, the diameter of micropores increased. When the current density is higher than 5 A/dm², the hydrate with flocculent structure is found on the edge of micropores indicating the higher current density could induce hydration to seal the micropores of coating at relatively low temperature in the silicate electrolyte solution. The thickness of MAO coating increased with the current density increasing. The electrochemical corrosion results showed that the MAO coating prepared at 6 A/dm² has the best corrosion resistance.