Abstract: Na₂WO₄ additive was added to the electrolyte of silicate system. The effect of concentration of Na₂WO₄ additive on surface morphology and properties of micro-arc oxidation ceramic film on LY12 aluminum alloy was studied by means of SEM, XRD, hardness test and electrochemical corrosion test. The results show that with the addition of Na₂WO₄, the microstructure of the film is changed, and the hardness of the film increases, the surface is smooth, and there are fewer small holes and a small amount of irregular white particles on the surface. With the increase of Na₂WO₄, the hardness of the film increases first and then decreases. When the Na₂WO₄ content is 4 g/L, the maximum hardness of the film is 440.3 HV0.3, which is increased by 272.3 HV0.3 compared with that of the substrate (about 168 HV0.3). XRD analysis shows that W element participates in the micro-arc oxidation process, and forms oxide WO₃. The ceramic layer mainly consists of α-Al₂O₃, γ-Al₂O₃ and WO₃. The electrochemical polarization curve analysis shows that addition of Na₂WO₄ effectively improves the corrosion resistance of the film, and the corrosion resistance is the best when the additive amount is 1 g/L, the corrosion potential is -532.0 mV and the corrosion current is 0.011 μA. The addition of Na₂WO₄ can effectively improve the surface morphology and properties of the ceramic film. The optimal addition amount of the Na₂WO₄additive is 4 g/L so as to obtain the comprehensive performance of the film.

Key words: LY12 aluminum alloy, micro-arc oxidation, silicate system, Na₂WO₄, ceramic film