Corrosion behavior of hot dip galvanized coating exposed in a simulated coastal-industrial atmosphere

The corrosion process of hot-dip galvanized coating in a simulated coastal-industrial atmosphere was investigated by means of an unsaturated dry-wet alternating cycle accelerated corrosion test. By using weight loss measurement and potentiodynamic polarization, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffractometry (XRD) analyzed corrosion behavior of hot-dip galvanized coating exposed after 24, 48,96, 192, 336, and 672 h. The results show that corrosion kinetics followed the empirical equation D=Btn, and there is a corrosion rate transition from corrosion acceleration to deceleration. Before 96 h the corrosion process is controlled by the cathode diffusion process, while after 96 h by the anodic. The protectiveness of corrosion products NaZn4SO4Cl(OH)6·6H2O and Zn12(OH)15Cl3(SO4)3·5H2O which containing Cl is worse than that of initial products Zn5(CO3)2(OH)6.