Improved corrosion resistance of electrogalvanized steel by a surface treatment with cerium, organic additive and niobium compound

摘要

This work investigates a new environmentally friendly passivation treatment for the corrosion protection of electrogalvanized steel. The passivation treatment tested was a multi-step process consisting of progressive immersion in solutions of: (ⅰ) hexahydrated cerium nitrate and an organic additive; (ⅱ) hydrogen peroxide (H_2O_2); (ⅲ) ammonium niobium oxalate (ANO) and the organic additive used in step (ⅰ), then drying and a final immersion in a bath of the organic additive sealant. The passivated surfaces were characterized by scanning electron microscopy (SEM) energy dispersive X-ray analysis (EDX), X-ray photonelectron spectroscopy (XPS) and X-ray diffraction. The surface treated samples were also tested for corrosion resistance using the salt spray test and electrochemical impedance spectroscopy in a NaCl 0.1 mol.L~(-1) solution for various exposure times. For comparison, the electrogalvanized steel was also passivated in a hexavalent chromium containing solution. The passive layer obtained by the new treatment showed higher impedances compared to that of the hexavalent chromium conversion coating for long periods of immersion.