PREPARATION OF MICROARC OXIDATION COATING ON (Al2O3-SiO2)sf/AZ91D MAGNESIUM MATRIX COMPOSITE AND ITS ELECTROCHEMICAL IMPEDANCE SPECTROSCOPIC ANALYSIS\par
ZHU Qingzhen1,2), XUE Wenbin1,2), LU Liang1), DU Jiancheng1,2), LIU Guanjun3), LI Wenfang3)
1) Key Laboratory of Beam Technology and Materials Modification of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875
2) Beijing Radiation Center, Beijing 100875
3) School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640
Cite this article:
ZHU Qingzhen XUE Wenbin LU Liang DU Jiancheng LIU Guanjun LI Wenfang. PREPARATION OF MICROARC OXIDATION COATING ON (Al2O3-SiO2)sf/AZ91D MAGNESIUM MATRIX COMPOSITE AND ITS ELECTROCHEMICAL IMPEDANCE SPECTROSCOPIC ANALYSIS\par. Acta Metall Sin, 2011, 47(1): 74-80.
Abstract A thick protective ceramic coating on 33% (Al2O3-SiO2)sf/AZ91D (volume fraction) magnesium matrix composite was prepared by the microarc oxidation (MAO) technique in silicate electrolyte. SEM, EDS and XRD were employed to analyze the surface morphology, composition and phase constituent of the coating, furthermore, the microhardness profile of the coating was also measured. The electrochemical corrosion properties of magnesium matrix composite before and after the MAO surface treatment were evaluated by electrochemical impedance spectroscopy (EIS), and the equivalent circuits corresponding to different immersion times were suggested. The results show that the fiber-reinforced composite surface is completely covered by the MAO coating. The ceramic coating mainly consists of MgO and Mg2SiO4 phases. The maximum microhardness of coating is up to 1017 HV. The electrochemical impedance modulus, |Z|, of the coated magnesium matrix composite increases significantly compared with bare composite, thus the magnesium matrix composite coated by MAO displays a good corrosion resistance. The occurrence of inductive loop in EIS of coated composite after 96 h immersion in 3.5% NaCl solution implies the pitting deterioration in the coating. The corrosion resistance of coated magnesium matrix composite is determined by the properties of inner compact layer of MAO coating.
