| A green sealing treatment for anodic film on Al substrate using pulsepower supply in solution containing aluminum sulfate was introduced inthis paper. The anodic film sealed by pulse current method excels directcurrent sealing in the corrosion resistance of anodic film in NaCl solution.The process of pulse current sealing is optimized according to studyingthe effects of pulse frequency, percent of negative current and seal timeon the corrosion resistance of anodic film.Potentiodynamic polarization technology was applied to study theanodic polarization behaviors of anodic oxide film sealed by differentmethods in neutral, acidic and alkaline NaCl solutions, respectively.These methods included the green pulse sealing, boiling water sealing,potassium dichromate sealing and nickel fluoride sealing. The resultsshow that the film sealed by pulse provided much the same corrosionresistance compared to the traditional sealing methods, and was suitable for different aluminum alloys.The corrosion behaviors of unsealed and sealed anodic film insodium chloride solutions were studied by means of electrochemicalimpedance spectroscopy. There is an auto-sealing process for theunsealed anodic oxide film in the beginning of immersion time, whichincreases R_p values and decreases C_p value. As immersion time furtherincrease, change of R and C for the pulse sealed anodic film in acidicsolution is more rapid than in neutral and alkaline solution, which showsthe anodic film by pulse sealing has better corrosion resistance in acidicsolution.The surface morphology was examined by scanning electronmicroscopy (SEM). The oxide film sealing by pulse method can passthrough 500h neutral salt fog test. The results show that pulse currentsealing is an environmentally friendly sealing method that may be analternative to potassium dichromate sealing.
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