Effect of NO 3 − Intercalation on Corrosion Resistance of Conversion Coated Zn-Al-CO 3 LDHs on Electrogalvanized Steel

Abstract

© The Author(s) 2018. To modify the corrosion protection provided by conversion coated Zn-Al-CO3layered double hydroxides (LDHs) on electrogalvanized steel sheets (EG steels), methods to intercalate NO3−during post treatment were explored and the effect of intercalation on corrosion resistance was evaluated. EG steels were immersed in a Na2Al2O4based solution to form a Zn-Al-CO3LDH conversion coating layer, and were then immersed in a NaNO3methanol solvent to intercalate NO3−. After 2 h of immersion, it was found that NO3−had completely exchanged with the originally intercalated CO32− anions in the conversion coated Zn-Al-CO3LDHs. Corrosion resistance measurements of the EG steel surfaces protected by the NO3−intercalated in the LDH layer were performed by a simple immersion test and a droplet test. When the samples were immersed in a large amount of 0.1 M NaCl, the corrosion resistance of the NO3−intercalated LDH layer was inferior to that of the control sample. In contrast, the samples that were exposed to a 100 μl droplet of 0.1 M NaCl displayed improved corrosion resistance. The difference in these results was attributed to the solubility of the LDH layer and the resulting effect on the release process of NO3−from the LDH layer.