The Process Of Alumnium Alloy Anodic Oxide Film Sealed By Green Sealing Method And Corrosion Resisitance Study

A new green sealing process of anodic oxide film of aluminum alloy was studied in this paper.The process is that anodic oxide film of aluminum alloy was sealed in the rare-earth salt solution,applied positive and negative pulse voltage.The influence of main was studied.The best parameters are as follow:sealing temperature is room temperature;pulse voltage is 800 mv-1200mv;pulse frequency is 50 Hz;the work ratio of positive and negative is 1:1;the duty cycle of positive and negative is 60 percent and 35 percent;concentration of rare earth salt is 1.5 g·L^-1-3.0 g·L^-1;time of sealing is 20-40 min.The corrosion resistance of the sealed anodic oxide film of aluminum alloy was investigated.Potentiodynamic polarization was applied to study the anodic polarization behaviors of sealed L3&LY12 aluminum alloy anodic oxide film by different methods in neutral,acidic and basic NaCl solutions,respectively.These methods included the green sealing,boiling water sealing,potassium dichromate sealing.The results show that the film sealed by pulse voltage provided much the same corrosion resistance compared to the traditional sealing methods.It was suitable for some aluminum alloys anodic oxide film.The corrosion behaviors of unsealed and sealed anodic oxide film in sodium chloride solutions were studied by means of electrochemical impedance spectroscopy.Porous layer impedance value and capacitive reactance value was studied by EIS.The aging experiment was studied on aluminum alloy anodic oxide film sealed by different methods with 1 mol·L^-1NaCl solution immersion.The results show that there is an auto-sealing process for the unsealed anodic oxide film in the beginning of immersion time.The Rp,Cp of aluminum alloy anodic oxide film after sealed did not changed significantly.The Rp,Cp of anodic oxide film sealed by pulse voltage changed obviously in acidic solution with sterilization time.It did not changed significantly in neutral and basic solution.It was demonstrated that the anodic oxide film sealed by pulse voltage has corrosion resistance in acidic solution.The anodic oxide film sealed by pulse voltage still has excellent corrosion resistance after immersion in 1 mol·L^-1NaCl solution for 30 days.The micro surface was examined by SEM.The surface composition was analysised by XPS.The results show that the Ce³⁺was on surface. Seal mechanism was inferred that the anodic oxide film was sealed by the Ce³⁺generation into the porous sediment to plug into porous layer.These results show that the pulse voltage sealing can substitute potassium dichromate sealing.The pulse voltage sealing is a non-pollution method.It is also a new green sealing method.