Effect of Na₂CO₃/C₆H₁₂O₆ in Electrolyte on Microstructure and Corrosion Resistance of AZ31 Magnesium Alloy Anodized Film

After adding different content of Na₂CO₃ and C₆H₁₂O₆ into NaOH-Na₂SiO₃-Na₂B₄O₇ basic electrolyte, AZ31 magnesium alloy was treated by direct current anodizing and then the microstructure and corrosion resistance in neutral salt spray of the magnesium alloy anodized film were studied. The results show that all magnesium alloy anodized film consisted of MgO and Mg₂SiO₄ phase. After adding Na₂CO₃ and C₆H₁₂O₆ into electrolyte, the micropores evenly distributed on the surface of the anodized film, and the size decreased; the thickness of the anodized film increased. When the mass concentration of Na₂CO₃ increased from 10 g·L^-1 to 30 g·L^-1, the size of micropores increased, and the thickness of anodized film decreased. When the mass concentration of C₆H₁₂O₆ increased from 5 g·L^-1 to 15 g·L^-1, the size of micropores decreased, and the thickness of anodized film increased. The main corrosion form of magnesium alloy anodized film was pitting, which presented a distribution of fluvial pattern. After adding 10 g·L^-1 Na₂CO₃ into the electrolyte, the micropores had the smallest size with the diameter of 1-3 μm, and the thickness of the anodized film reached 16 μm; the anodized film had relatively good corrosion resistance.