Pitting corrosion of Zn and Zn-Al coated steels in pH 2 to 12 NaCl solutions

Corrosion behavior of hard zinc, Zn-5% Al (Galfan), and Zn-55% Al alloy (Zincalume or Galvalume) coated steels was studied using cyclic voltammetry and potential scan/hold technique in the presence of 0.10- 0.90 mol L-1 NaCl over a pH range of 2 to 12. Influence of chloride concentration and electrolyte pH on pitting potential values of the above three types of specimens were examined. On the basis of the electrochemical, scanning electron microscopy with energy dispersive X-ray spectroscopy, and chemical equilibria data obtained from hard zinc, a pitting corrosion mechanism involving a series of processes from anion competitive adsorption to penetration to nucleation and growth was proposed.