The Effect Of Anodizing And Sealing Process On Corrosion Resistance Of 2A12 Aluminum

Anodic films were prepared on 2A12 aluminum alloy in oxalic acid in this paper. The influence of additives on the hardness, thickness and the anti-corrosion of the anodic films were examined. And the aluminum anodic oxide films were sealed with cerium salt solution and aluminum phosphate to further improve their corrosion resistance. Through the studying of the effect of the parameters on the sealing treatment on corrosion resistance of the anodic oxide films by electrochemical impedance spectroscope (EIS), the optimal process were obtained. Moreover, a new composite sealing treatment of cerium salt-phosphate was proposed on the basis of single treatment with cerium salt solution and aluminum phosphate.Compared with single oxalic acid, the anodizing current density reduced in the solution with additive of sulfosalicyl, while it increased in the solution with sodium dihydrogen phosphate. The anodic film obtained in the oxalic acid with both sulfosalicyl and sodium dihydrogen phosphate performed better corrosion resistance than that obtained in oxalic acid without additives or with single sulfosalicyl or sodium dihydrogen phosphate. The film was of porous-type with 10-20 nm in pore size and the continuity of the film was destroyed by the formation of large-sized etch pits caused by the second phase.The sealing effect increased with the increasing of sealing temperature in a certain range when the films sealed in the cerium salt solution. And when the temperature reached 100 ℃, the sealing effect was poor because of the nature changing of the sealing solution. The sealing effece improved with the extension of sealing time when the films sealed in the in the cerium salt solution with temperature of 30 ℃ and 60 ℃. The optimal process was obtained by the study of the factors, that the temperature is 60 ℃, the sealing time was 150 min.With the increasing of the number of depositing, the sealing effect increased first and then decreased when the concentration of aluminum dihydrogen phosphate used to sealing the anodic films was the same, while the sealing effect had also the same trend when the variable quantity was the concentration of aluminum dihydrogen phosphate. The optimal process was as follow, the concentration of aluminum dihydrogen phosphate was 10%, and the number of depositing was four.Cerium salts-phosphate Composite sealing treatment was applied by the optimal process of sealing with Cerium salts and aluminum dihydrogen phosphate, compared to the single sealing treatment with Cerium salts or aluminum dihydrogen phosphate, and the traditional sealing treatment of boling water sealing, the composite sealing treatment could provide the best corrosion resistance for the aluminum alloy and the effect of the composite sealing treatment could last longer than another sealing methods used in this paper. This method could be a new sealing treatment of aluminum anodic oxide film.