Abstract: The phase composition and electrochemical performances of microarc oxidation(MAO) films prepared on AZ91D alloy by using step-down current method in a phosphate electrolyte(P-film) and silicate electrolyte(Si-film) were studied. The results show that P-film is mainly composed of Mg, MgAl₂O₄ and MgO,  and Si-film is composed of Mg₂SiO₄ and MgO. There clearly exists a fluoride-enriched zone with the thickness of about 1-2μm for P-film and 0.7-1μm for Si-film at the MAO coating/substrate interface. The electrochemical tests show that both P-film and Si-film can enhance the corrosion resistance of AZ91D magnesium alloy significantly. The corrosion failure process of the two films in 5%(mass fraction) NaCl solution is quite different.

Key words: AZ91D alloy; electrolyte; microarc oxidation; electrochemical performance