Preparation and electrochemical characteristics of trivalent chromium-zirconium hybrid coatings on 6063 aluminum alloy

To improve the corrosion resistance of trivalent chromium coatings,trivalent chromium-zirconium hybrid coatings were prepared on 6063 aluminum alloy by using chromic potassium sulfate and zirconium sulfate,and phosphoric acid.Polarization curves and electrochemical impedance spectroscopy(EIS)were used to investigate the electrochemical characteristics of chromium-zirconium hybrid coatings formed in plating solutions of different concentrations of zirconium sulfate,and better corrosion resistance was confirmed.Compared with the coatings without zirconium sulfate plating and bare aluminum alloy,polarization curves showed that the hybrid coatings formed in 0.8—1.2 g·L-1 Zr(SO4)2 plating solution had more positive corrosion potential,and lower corrosion current density.Electrochemical parameters of EIS indicated that the hybrid coatings had higher resistance and charge transfer resistance.The morphology and composition of the coatings were examined by SEM and EDS,respectively.The results showed that the morphology of coatings remained almost unchanged and the coatings mainly consisted of Cr,Zr,P,and O after addition of zirconium sulfate,and the chromium-zirconium hybrid coatings were formed on 6063 Al alloy.