Effect of Rare Earth Chloride on Corrosion Resistance of in Situ Phosphatizing Organic Coatings on 6061 Aluminum Alloy

In situ phosphatizing of organic coatings is a one-step self-phosphating process, in which the formation of metal phosphate layer on the substrate surface and the curing of organic paint film take place simultaneously instead of multi-step process. In this study, different rare earth(Re) chlorides were incorporated into in situ phosphatizing solution and organic coatings were prepared. Polarization curves and electrochemical impedance spectroscopy (EIS) were used to characterize the characteristics of organic coatings. The results indicate that the rare earth which has good stability as a phosphating accelerator can improve the efficiency and quality of phosphate. In situ phosphatizing organic coatings prepared by incorporating rare earth chloride can improve the corrosion resistance of 6061 aluminum alloy in 3.5% NaCl solution effectively. When 0.2% (mass ratio) LaCl3 was addied to in situ phosphatizing solution, in situ phosphatizing organic coatings had the best performance and a good protection for aluminum alloy substrate. Salt-water immersion test results indicated that the bond between in situ phosphatizing organic coatings and aluminum alloy substrate was enhanced by incorporating rare earth chloride.