| 2024 aluminum alloy is A1-Cu-Mg alloy with high strength and hardness,and it also has good plasticity and other excellent properties.Therefore,it has been widely used in commercial and civil products,space aviation,transportation and many other fields.But 2024 aluminum alloy is very sensitive in the corrosive medium environment.For example,pitting,denudation,intergranular corrosion and stress corrosion can be found,which eventually lead to the failure of aluminum alloy parts.Based on the analysis of Tafel polarization curve,electrochemical impedance spectroscopy and the simulation by equivalent circuit,the corrosion resistance of anodic oxide film formed on aluminum alloy in 3.5%NaCl solution is studied.At first,the optimum first and second oxidation times were investigated on the film by two-step anodization in oxalic acid electrolyte.In order to further improve its corrosion resistance,sealing treatment on the anodic oxide film was carried out.The influence of the sealing parameters of phytic acid was explored,and the best sealing parameters were obtained.Two-step anodizing process can be seen as an effective way to form a continued adherent alumina layer on the surface of aluminum alloy to enhance its corrosion resistance.The film with excellent corrosion resistance can be obtained by changing the first and the second oxidation time.2024 aluminum alloy was used as the research object,and anodic oxidation film was prepared by two-step anodization in oxalic acid electrolyte.The experiment shows that the optimum time of first anodization is 45 min,and the optimum time of second anodization is 120 min.The oxidation film formed on the first oxidation time of 45 min will get better periodic pit after removing oxide layer,and will also be benefit for the oxide layer growth of the second anodization.Too long oxidation time will lead to the rough,loose and easy falling off of the oxide film.Besides,it will also increase the dissolution rate and porosity of the oxide film.All these factors may lead to the reduction of the corrosion resistance of the oxide film on the aluminum alloy.Under the premise of 40 g L-1 oxalic acid electrolyte,oxidation temperature of 15°C,and anodic oxidation voltage of 40 V,the first/second oxidation time for 45min/120 min was considered to be the optimum condition as it had the excellent corrosion resistance.The corrosion resistance of the aluminum oxalic acid anodic oxide film is greatly improved by the sealing of the phytic acid.For the oxide film formed on the electrolyte of oxalic acid,the optimum technology of phytic acid sealing is the phytic acid of 2.5wt.%,sealing time of 15 min and sealing temperature of 90?.The unsealed anodic oxide film presents a porous structure.While the sealing treatment of phytic acid not only fills these micropores,but also forms a certain thickness of phytic acid conversion film on its surface.Moreover,for anodic oxide film formed on the electrolyte of oxalic acid,the effect of the phytic acid sealing is better than that of boiling water sealing. |
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