Corrosion Behavior of Passivation Coatings on Hot-Dipping Galvanized Steel Prepared from Trivalent Chromium Salt

The passivation solutions composed of bivalent chromium salt (TC) and trivalent chromium salt-acrylic resin (TCA) were used to replace toxic chromate passivation solution for the surface modification of hot - dipping galvanized steel. The corrosion behavior ofthe resulting passivation coatings was evaluated using neutral salt -spraying test and electrochemical test, and the anticorrosion mechanism of the passivation coatings was discussed. Moreover, the mi crostructures of the passivation coatings were observed using a scanning electron microscope, while the chemical states of the typical elements in the coatings were analyzed using an X-ray photoe lectron spectroscope. It was found that the corrosion resistance of the hot-dipping galvanized steel was effectively increased after passivation with both TC and TCA solutions, and the TCA passivation coating had similar inhibitive efficiency as chromate passivation coating. Besides, some micro-cracks were observed in the TC passivation coating, but the TCA passivation coating was uniform and compact and showed network - cystiform morphology ascribed to a-crylic resin, which could contribute to greatly increasing the corrosion resistance of the TCA coating. In addition, the chromium in both the TC and TCA coatings existed as trivalent Cr, i. e. , Cr(OH)3 or CrOOH, and quadrivalence C and quinquevalence N were also detected in the TCA passivation coating.