Rare Earth Lanthanum Passivation Technology of Galvanized Steel

The process of rare earth lanthanum conversion coating for galvanized steel was studied by orthogonal experiment. The optimized passivation parameters were obtained as follows. the concentration of La(NO3) 30 g/L, H2O2 20 ml/L, pH 4 and passivation at 40 ℃ for 30 s. The corrosion resistance was examined by weight loss test, neutral salt spray test and electrochemical impedance spectruscopy. The results showed that the corrosion impedance of the pretreated sample was significantly improved, the corrosion rate was decreased by one order of magnitude, and the anti-white rust time was 54 h. Scanning electron microscopy (SEM) showed that the conversion coat covered the surface of zinc compactly.