Electrochemical performance of microarc oxidation films formed on AZ91D alloy in two group electrolytes
(State Key Laboratory of Die and Mould Technology,
Huazhong University of Science and Technology, Wuhan 430074, China)
Huazhong University of Science and Technology, Wuhan 430074, China)
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