Sol-gel Doped With Cerium Salt And Phosphate Treatment For The Corrosion Protection Of Anodic Oxide Film Of Aluminum Alloy

Anodic films were prepared on the surface of 2024 aluminum alloy in oxalic acid,and this films comprised a close-packed array of hexagonal columnar cells perpendiclar to the substrate.And the continuity of the film was destroyed by the formation of large-sized etch pits caused by the second phase.Therefore,the oxide films must be sealed.In early study,a treatment process based on the use of sol-gel film was applied on anodic oxide films,but the long-term corrosion resistance is poor.So we focused on the basis of the sealing treatment to enhance the long-term corrosion resistance method.In this paper,the Al₂O₃ and ZrO₂ sol-gel coatings doped with cerium salt depositing on anodic oxide film of aluminum alloy.The effects of drying temperature,drying time and cerium salt content on the corrosion resistance of the anodic oxide film were studied.Moreover,the dense aluminum phosphate was fabricated on the basis of sol treatment,and the effect of phosphate concentration was studied.Finally,the optimal composite sealing process was obtained.The corrosion behavior of the Al₂O₃ and ZrO₂ sol-gel coatings doped with cerium salt were deposited on anodic oxide film of aluminum alloy were investigated by using electrochemical impedance spectroscopy?EIS?and immersion tests.The results show that when the curing time is constant,the corrosion resistance increases with the curing temperature.When the curing temperature is constant,the corrosion resistance first increases and then decreases with the increase of the curing time.When the concentration of cerium nitrate in the sol was 0.1 M,and thermal treatment was carried out at 250? for 30 min,the corrosion resistance of the film was the best.After 360 h of immersion in the 3.5%NaCl solutio1,the |Z|0.01HZ is around 10⁵ ?· cm².The corrosion resistance of the anodic oxidation film sealing with Al₂O₃ and ZrO₂ sol doped with cerium nitrate is significantly higher than that of the film sealed by Al₂O₃ and ZrO₂ sol,and this phenomenon is mainly caused by the self-sealing effect of cerium nitrate.Under the identical sealing process,corrosion resistance of the anodic films sealed with Al₂O₃ sol performed a little better than with ZrO₂ sol.An aluminum phosphate top coat was then applied as a barrier layer against corrosion species.The results show that the double sealing treatment can further enhance the sealing effect of the anodic oxide film of aluminum alloy,and its corrosion resistance is better than the traditional boiling water.The optimal process was as follow,the concentration of phosphate was 10%,and the concentration of cerium nitrate in the sol was 0.5 M.After 480 h of immersion in the 3.5%NaCl solution,the |Z|0.01Hz is around 10⁶ ?· cm²...