Inquiry On Anodizing Process Of 3005 Aluminum Alloy In Organic-inorganic Mixed Acid System And Its Properties

3005 aluminum is aluminum-manganese alloy, which has many advantages such as good corrosion resistance, high thermal conductivity and excellent machinability. It is widely used in kitchen supplies, packaging materials, construction materials and heat exchanger materials. Oxide film is formed on aluminum alloy by anodic oxidation treatment. The film is thick and dense, which can greatly improve the corrosion resistance, wear resistance and hardness of aluminum alloy. However, the anodized aluminum oxide film is an amphoteric oxide, prone to dissolve and lose the ability to protect the aluminum body in an acidic or alkaline medium, so that the scope of application of aluminum alloys is subjected to certain restrictions.In the thesis, a certain concentration of inorganic acid H2SO4 based mixed acid electrolyte containing different proportions of organic acids A(polyhydroxy organic acid) and B(dibasic organic acid) was used. 3005 aluminum alloy was anodized in the above electrolyte under constant current density. The effect of different proportions of organic acids A and B on the anodized films' thickness and morphology was studied. In order to determine the optimum ratio of organic acid A to B, electrochemical impedance method was used to compare the alkali resistance of oxide films. The composition of optimum mixed acid electrolyte is as follows: organic acid A: 60 g/L, organic acid B: 40 g/L, inorganic acid H2SO4: 60 ml/L.The influences of current density, oxidation time and electrolyte on the thickness and corrosion resistance of the obtained oxide film under the above optimum electrolyte were optimized. The electrochemical impedance method was used to determine the alkali resistance of the oxide film. The optimal parameters were: current density 1.5 A/dm2,oxidation time 30 min,electrolyte temperature 5±2 ?. Alkali resistance of the oxide film obtained from mixed acid and traditional sulfuric acid was compared by electrochemical impedance method. The result shows that the oxide film obtained from mixed acid has better alkali resistance.Under optimum conditions, the dibasic organic acid B was replaced by dibasic organic acid C and D, respectively. The influences of different organic acids on oxide film thickness and microscopic morphology were studied. The comparison result shows that the deposition efficiency: dibasic organic acid C>D>B, alkaline resistance of the film: dibasic organic acid D> B> C.The anodic oxide film obtained by mixed acid electrolyte with organic acid B, C, and D, respectively, was sealed by boiling water. The morphology of sealed film was then observed by SEM. Alkali resistance was determined by electrochemical method. The result shows that alkali resistance of the film can be improved. Alkali resistance of sealed film with different dibasic organic acid: D> B> C. The trend is consistent with unsealed film. Finally, in alkali solution immersion test, the corrosion behavior of sealed anodized films at different time was observed. SEM was used to observe the film's microstructure change. The microscopic etching process of the aluminum oxide films formed in mixed acid electrolyte in alkaline was analyzed and discussed.