Effecct of Buried Depth on Corrosion Behavior of Hot Dip Galvanized Steels in Soil

The effects of buried depth on corrosion behavior of hot dip galvanized steel were investigated by electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN). The growth process of corrosion products and the variation law of corrosion type with time were analyzed. Scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD) were used to observe and analyze the microstructure and chemical composition of corrosion products, and the corrosion mechanism of the galvanized steel was also discussed. The results showed that the corrosion rate of hot dip galvanized steel in 45 cm deep soil was obviously higher than that in 25 cm and 35 cm deep soil. In 25 cm deep soil, the hot dip galvanized steel had a certain degree of pitting in the early stage, and the protective film of xZnCO₃·yZn(OH)₂ was formed on the surface after corrosion for 70 d. In 35cm deep soil, CaZn(OH)₃₂ protective film attaching to the matrix tightly was formed on the surface after corrosion for 70 d, and the growth rate of the film was slow. In 45 cm depth of soil, pitting and uniform corrosion occurred alternately, corrosion of the galvanized steel was serious, xZnCl₂·yZn(OH)₂ and ZnO were formed on the surface sporadically.