Effect of Corrosion Inhibitors on Chromate-free Passivation of Hot-Dip Galvanized Steel

Abstract

Commercially available passivation methods for white-rust protection of Hot-Dip Galvanized steel have been applied for chromate passivation. However, hexavalent chromium (Cr-VI) is highly toxic and carcinogenic. Therefore, in this paper, we put forth a new means for white-rust protection of Hot-Dip Galvanized steel based on the effects of corrosion inhibitors. In this study, the passivation solution combines the advantages of inorganic salt passivation, silane passivation and resin passivation. The corrosion resistance of the inorganic and organic composite passivation films with corrosion inhibitors was determined by a neutral salt spray test and electrochemical Tafel polarization curves. The surface chemistry of the coatings was monitored by scanning electron microscopy (SEM), X-ray Photoelectron spectroscopy (XPS) and Fourier transform infrared reflection absorption spectroscopy (FTIR). And further studying on the formation mechanism of the passivation film was carried out. The SEM indicated that the top surface of the passivation film was transparent, smooth, uniform and compact. The XPS and FTIR results showed that the passivation film consisted mainly of organic functional groups including-(CH₂)n-, -OH, N-H, C=O, C-Si, C-O-C, C-N, Si-O-Si, Si-O-C and so on. The corrosion resistance of passivation film with corrosion inhibitors was significantly improved than that of the passivation film without corrosion inhibitor. After 96h of the corrosion test, the corrosion area was found to be less than 5 %, which indicated that the passivation film greatly improved the corrosion resistance of the hot-dip galvanized sheet, and exhibited a very good protective effect so that can met some industrial applications.

DOI: http://dx.doi.org/10.5755/j01.ms.24.3.16330