Corrosion behavior of field-exposed electrogalvanized steel plate in marine atmosphere

Corrosion behavior of electrogalvanized steel plate exposed to atmospheres at Qingdao located at the East coast of China and Xishuangbanna, an area of tropical rainforest climate, located at Yunnan province respectively for 2 a was investigated by means of weight- loss measurement, macro-morphology observation, SEM and XRD etc. The electrochemical behavior of the plate in solutions with different chloride concentration was studied by electrochemical impedance spectroscopy. The results showed that the corrosion rates of the steel exposed to the atmospheres at Qingdao and Xishuangbanna are 0.76 and 0.1935 μm/a respectively. Local red rust was observed on the surface of the steel plate exposed to Qingdao atmosphere, which consists of Zn₅(OH)₈Cl₂H₂O, ZnO and Zn(OH)₂. In the atmosphere at Xishuangbanna, the main corrosion products are 2ZnCO₃·3Zn(OH)₂, ZnO and Zn(OH)₂. Inhomogeneous general corrosion occurs in the two test areas and the electrogalvanized steel plate suffered more severely from corrosion in the atmosphere at Qingdao because of the influence of Cl^-.