Corrosion study on Al-rich metal-coated steel by odd random phase multisine electrochemical impedance spectroscopy

Galvanized steel is widely used in transportation and industry. However, the corrosion performance of these products is highly affected while exposed to chloride-containing environments. One alternative is Al-rich metal coatings which are known to notably improve the corrosion protection of the steel substrate by the enhanced barrier properties provided by Al. Although hot dip aluminum-based coatings on steel are nowadays used for many applications, little is known about the electrochemical behaviour of these coatings. This work studies the corrosion behaviour of Al-containing metal coated steel. Odd random phase multisine electrochemical impedance spectroscopy (ORP-EIS) is used for monitoring the corrosion evolution under continuous immersion in a NaCl solution. This technique allows a rapid screening of corrosion processes due to the reduced measurement time with respect to conventional single sine techniques. Extra information concerning linearity, stationarity and noise level is also supplied and can be valuable for further data quality evaluation and fitting. Different equivalent electrical circuits are proposed and their validity is discussed, not only based on physical phenomena but also taking the quality of the obtained data and the statistical evaluation of the fittings into account.