New Passivating Method to Galvanized Zn Coatings on Steel Substrate
As the increasing environmental awareness, to explore no-chromium passivation technique on galvanized Zn coatings becomes one of the most urgent affair. In this paper, one kind of silicate passivation technics was invented and by which method silicate conversion film on galvanized Zn coatings with satisfactory property was got. It is found that solution composition and operating conditions of passivation affect the property of conversion film markedly, and the optimal technics is: Na2SiO3 20 g/L, H2SO4 5 mL/L, HNO3 5 mL/L, H2O2 10 ml/L, pH 2.0, passivation time 20 s, temperature 25°C. The corrosion resistance of galvanized Zn coatings with different passivated method, including no passivated, Cr(VI) passivated, Cr(III) passivated and silicate passivated, were investigated by NSS test (5% Neutral Salt Spray). The silicate conversion film can keep no rust for 72 h and obviously shows the best property. All the results show that silicate passivation can provide galvanized Zn coatings superior anti-corrosion performance, so this new technics can replace the conventional chromate passivation technology to avoid the pollution of chromium and has a wider application in future.
Y. Y. Fan et al., "New Passivating Method to Galvanized Zn Coatings on Steel Substrate", Advanced Materials Research, Vols. 163-167, pp. 4555-4558, 2011