Blue-white trivalent chromium passivation process on zinc coating with high corrosion resistance

An environment-friendly trivalent chromium blue-white passivation process for zinc coatings was developed. The effects of bath components such as CrCl3 ·6H2O, Na3C6H5O7 , NaNO3 and cobalt salt, and process parameters including pH and temperature on the appearance and corrosion resistance of passivation coating were studied. The optimal process conditions are as follows: CrCl3·6H2O 48 g/L, NaNO3 20 g/L, Na3C6H5O7 18 g/L, cobalt salt 18 g/L, room temperature, pH 1.5, and passivation time 8 s. The passivation coating obtained under the optimal process conditions is bright and blue-white, uniform, smooth and compact, and has better corrosion resistance than zinc coating.