Corrosion resistance of Fe–Zn surfaces of galvannealed steel revealed after coulometric stripping in acid, alkaline and saline media

Abstract

The corrosion of galvannealed steel revealed three different Fe-Zn surfaces on the steel substrate, and each surface showed a different corrosion behaviour in a given environment. In order to evaluate the corrosion behaviour of each revealed surface, the electrochemical impedance spectroscopy (EIS) technique was performed in acid, alkaline and saline media containing chlorides and sulphates. The Mossbauer spectroscopy was also used to elucidate the iron phases on each surface, and these results identified the delta phase on all surfaces obtained after coulometric dissolution of galvannealed steels. In the hydrochloric acid and sodium chloride solution, the outer surface richest in zinc showed the highest polarisation resistance among the surfaces obtained using coulometric stripping of galvannealed steel, and the corrosive process occurred on the electrode surface. In the alkaline solution, the inner layer showed the highest polarisation resistance among the surfaces obtained after dissolution of galvannealed steel, and the equivalent circuit fitted to the EIS data is characteristic of a corrosion of a porous layer.