Study Of Growing Process And Corrosion Resistance Properties Of Ceramic Coatings Formed By Micro ARC Oxidation On Magnesium Alloys

The growing process and mechanism of ceramic coatings formed by micro-arc oxidation on magnesium alloys were studied by the analysis of the rate of growth, surface and cross-section morphology, phase constitutes for ceramic coatings. The regularity influenced conductivity solutions and energy parameter on corrosion resistance of ceramic coatings and the corrosion resistance of ceramic coatings of process optimization was analyzed by the alt spray tests and the galvano-chemistry tests. The corrosion resistance of ceramic coatings of micro-arc oxidation and chromate and anode coating was compared.The result indicates that the coating grows in the following steps, i.e., the stage of anodic deposition, micro-arc oxidation and local arc light. In the first stage of anodic deposition, the flocculent oxidation film deposits and extends on the surface of magnesium alloy. In the stage of micro-arc oxidation and local arc light, the coating occurs plasma discharge because of plasma chemistry and galvana-chemistry. As oxidation time increases, the thickness of ceramic coating represents semi-parabolic growth. The micro-arc oxidation ceramic coating was made of Mg, MgO MgAl2O4 Mg2SiO4 and amorphism phase. The pH value can decide the formation of coatings. The pH value to form coatings ranges from 12.3 to 14.5 for MB8 magnesium alloys. The growth rate of ceramic coatings is fast with the conductivity of solution hoisted.With increasing the conductivity, the corrosion resistance of the coatings increases, and improved best at the conductivity of 4.0-5.5 (m)-1 . The control of electrical parameter plays a key role on the growth rate and corrosion resistance properties of ceramic coatings. The more current density played on the ceramic coatings is, the faster grow rate of ceramic coatings is. With frequency and duty cycle increasing, the grow:rate of ceramic coatings is constant nearly. But with frequency increasing, the corrosion resistance of ceramic coating increases. With duty cycle increasing, the corrosion resistance of ceramic coating reduces. The key to get compact and corrosion resistance ceramic coatings is to control the electrical parameter in different growth moment. The corrosion resistance of micro arc oxidation ceramic coating is better than the corrosion resistance of chromate and anode coating.