Comparative EIS Study on Atmospheric Corrosion Behavior of Zinc-Aluminum Coated Steels under Cyclic Wet-Dry Conditions

Due to the excellent anticorrosion performance, galvanized steels are widely used in a variety of structural applications for corrosion protection of steel structure exposed to atmospheric environment, especially marine atmosphere. In this work, the corrosion behavior of two representative zinc-aluminum hot-dip coated steels, Galvalume(GL) and Galfan(GF), under cyclic wet-dry conditions, was investigated by weight loss method and electrochemical impedance spectroscopy(EIS) measurement. The wet-dry cycle tests were carried out by exposure to alternate conditions of 1h immersion in seawater and drying for 3h and 11h at 298K and 60% relative humidity (RH). During the wet-dry cycles, the polarization resistance was continuously monitored and its reciprocal was considered as an index of corrosion rate. Results show that the anticorrosion performance of GL coating was better than that of GF coating in all tests. The effects of the formation of stable simonkolleite layer and other influence parameters, such as elemental composition of coating materials, on the corrosion of two coated steels were discussed.