Study on environmental corrosion performance of hot dip galvanizing coating

Abstract

In order to analyze the influence of environmental factors on the corrosion resistance of hot-dip galvanized coating, a naturally clean environment and thermal shock treatment were used to simulate the service conditions of products. The surface state and zinc layer thickness of hot-dip galvanized coating under two process conditions were detected. Salt spray corrosion and electrochemical corrosion tests were carried out on hot-dip galvanized coatings. The phase and microstructure of the coating were analyzed by XRD, OM, and SEM. The results show that the hot-dip galvanized coating has a good corrosion protection effect in a naturally clean environment. After thermal shock treatment, cracks in the coating are more likely to occur. With the increase of thermal shock time, the depth of crack on the surface of the coating increases, so the corrosion protection effect of the coating decreases obviously. For the thermal shock treatment of 10-30 days, the coating performance enters the corrosion stability period, and the thickness decreases very little, but when the time exceeds 30 days, the corrosion of the coating accelerates sharply. Electrochemical corrosion shows that the hot-dip galvanized coating has typical coating protection double capacitive reactance curve, and the polar protection effect is good. When the thermal shock treatment time is 30 days, the dense oxide on the coating surface has the best protection effect against corrosion. At this time, the self corrosion current is the smallest and the impedance radius is the largest. When the thermal shock treatment time exceeds 40 days, the cracks on the coating surface will expand to the substrate, and the corrosion protection effect of the coating may fail. So, the corrosion protection effect of hot-dip galvanized coating is limited in the current situation of frequent extreme environments and intensified environmental pollution.