Electrochemical behaviour of zinc-iron intermetallic compounds in an aqueous solution containing NaCl and ZnSO4

Fe-Zn alloys have widespread technological applications, especially in the automotive industry with galvannealed steel sheets. Pure and homogeneous intermetallic zinc-iron phases were fabricated and characterized for their metallurgical and physical properties. The electrochemical behaviour of these phases was studied in a chloride-sulfate solution generally used to characterize galvannealed coatings on steel. Selective dissolution occurred for the zinc-rich zeta and delta phases. This mechanism induced an iron enrichment of the surface and caused a modification of the electrochemical behaviour of the sample. A film of corrosion products, developed during the coulometric anodic dissolution of galvannealed steel sheets, seems to be related to this surface change. The study confirmed the previous results and showed that electrochemical stripping of the galvannealed coating is not convenient, in this electrolyte, for accurate determination of the structure of the coatings. (C) 1997 Elsevier Science Ltd.