Research Progress of Micro-arc Oxidation in Aluminum Alloy under the Phosphate system

Aluminum alloy has the advantages of low density, high strength and good plasticity. It has a wide application prospect in aerospace, mechanical electronics, vehicle ships and other fields. However, aluminum alloy surface has low hardness and poor corrosion resistance, which limit its wide application. Using micro-arc oxidation under phosphate electrolytic system to form oxide coating on aluminum alloy surface, it can effectively improve the surface hardness and corrosion resistance, and is a hot surface treatment technology in recent years. In this paper, the research process and the mechanism of micro-arc oxidation are introduced. Mainly summarizes the characteristics of micro-arc oxidation of aluminum alloy under single phosphates such as sodium hexametaphosphate, sodium dihydrogen phosphate, etc on surface topography, phase composition, the coating of hardness and thickness, corrosion resistance, as well as these characteristics in its composite system. It is indicated that micro-arc oxidation of aluminum alloy under the current phosphate system has some problems, such as the differences in the mechanism of electrolyte due to the different content of Si, Zn, Mn and other factors in various grades of aluminum alloy, the difficulty in the partial micro-arc oxidation treatment in the local region of large aluminum alloy parts, so as to result in the nonuniform micro-arc oxide coating after the treatment, which can decrease the fatigue resistance of the base coating in the thickness range, and the anti-fatigue property of the substrate coating will be reduced within a certain thickness range. Future research also needs to continue to explore the effects of various components in the phosphate electrolytic liquid system, the mechanism of interaction between electrolyte and matrix aluminum alloy, and the effects of matrix aluminum alloy elements on micro-arc oxidation process.