Correlation between Applied Voltage and Electrochemical Properties of Micro Arc Oxidation Coatings Formed on AZ31B Magnesium Alloy

摘要

The correlation between the electrical parameter of applied voltage and the coating properties, especially the electrochemical properties of micro arc oxidation coating layer was studied in environmental friendly electrolyte under single-polar pulse power supply. The coating surface morphology and corrosion resistance was characterized by atomic force microscope (AFM)and electrochemical method. The coating thickness and the pores in the coating layer grow with increasing the applied voltage;;also the surface becomes rougher at higher voltages. In the voltage range of 240 V to 320 V, the relative optimal voltage parameter is 260 V, which presents the smallest corrosion current density, three orders of magnitude lower than that of bare Mg substrate and the highest coating impedance value among all coatings. With increasing applied voltage from 240 V to 260 V, the corrosion resistance was improved significantly;;then decreased slightly at higher voltages of 280 V to 320 V. The impedance spectroscopy fitting results show that the voltage parameter has more effect on the inner layer than on the outer layer of micro arc oxidation coatings and the coating property is more dependent on the compact inner layer.