Optimisation of electrochemical stripping of galvannealed interstitial free steels

Abstract

Hot dip galvanised steels with thermal treatment or galvannealed steels are used in automotive industries because of their properties of weldability, workability and corrosion resistance. The galvannealed steels show three iron–zinc phases: zeta, delta and gamma. The distribution and concentration of iron–zinc phases affect the quality of the zinc layer and can produce stamping and welding problems. In the present work, the optimisation study of the electrochemical stripping process of industrial galvannealed steel was performed. The effect of electrolyte, pH, current density and scan rate was evaluated. The best resolution of the potential levels in the electrochemical dissolution curves was obtained for the zinc sulphate heptahydrate and sodium chloride aqueous solution, with a current density of 2 mA cm⁻² and pH 4·5. Each sample surface obtained by using electrochemical stripping was analysed using X-ray diffraction and scanning electron microscopy.

Keywords:

• Iron–zinc phases
• Electrochemical dissolution
• Cyclic voltammetry
• Galvannealed steel

The authors of this work would like to thank the National Council of Scientific and Technological Development (CNPq), the Coordination of Improvement of Superior Level Staff (CAPES) and the Foundation of Research Support of the State of Minas Gerais (FAPEMIG), as well as USIMINAS, an Industrial Group, for supporting this research.