Study on microstructure and electrochemical corrosion behavior of ζ-FeZn13 phase layer in hot-dip galvanized coating

Abstract

In this study, the electrochemical corrosion behavior of outburst and flat ζ-FeZn13 phase layers was investigated using scanning electron microscopy, field emission scanning electron microscopy, electrochemical workstation, and Raman spectroscopy instrument. The ζ phase layer is composed of the η phase, coarse ζ phase, and fine ζ phase. Their corrosion potential is Eη-Zn=-1.140±0.003 V, Efine-ζ=-1.052±0.003 V, and Ecoarse-ζ=-1.036±0.002 V. The presence of fine ζ phases can form a thick passivation film on the surface of the coating. The thickness of the passivation film for the outburst and flat ζ phase layers is 5.31 nm and 6.47 nm, respectively. The more uniform the distribution of fine ζ phases, the thicker the passivation film. The corrosion types of the outburst phase layer are mainly local corrosion and pitting corrosion, and the flat phase layer is mainly uniform corrosion. The corrosion products of η phase are ε-Zn(OH)2, 4Zn(OH)2.ZnCl2, Zn5(CO3)2(OH)6, and Zn5(Cl2)(OH)8.H2O. The corrosion products of ζ phase are Fe2O3, ZnO, and Zn(OH)2.