Optimization Study of Compound Electrolytes for Aluminum Alloy Micro-Arc Oxidation

For obtaining a thick ceramic coating with good film-forming and wear resistance, a new type of composite electrolyte was composed of sodium phosphate and sodium hexametaphosphate as the basic electrolytes, while sodium tungstate and sodium tetraborate were added as additives. In this composite electrolyte system, micro-arc oxidation treatment was performed on 1060 aluminum alloy. Using the coating thickness and surface porosity as optimization indicators, the electrolyte formula was optimized using the L9(34) orthogonal test. Meanwhile, the microstructure, surface porosity, phase composition, thickness, microhardness and wear resistance of ceramic coatings prepared under this electrolyte formula were studied systematically. Results showed that the ceramic coating prepared with a formula of Na3PO4 concentration of 32.0 g/L, Na2B4O7 concentration of 16.0 g/L, Na2WO4 concentration of 4.5 g/L and(NaPO3)6 concentration of 30.0 g/L had the structure with uniform micropores and dense film layer, the thickness of 22.8 μm, the porosity of 3.86%, and the microhardness of 475 HV. Furthermore, the wear resistance of the coating was significantly improved compared to the substrate, and the ceramic coating were mainly composed of γ-Al2O3 and a small amount of α-Al2O3 composition.