Studying phosphate corrosion inhibition at the cut edge of coil coated galvanized steel using the SVET and EIS

The work deals with the effect of sodium phosphate on the corrosion at the cut edge of electrogalvanized steel, studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET). Mapping of the ionic currents revealed that in non-inhibiting solution, the cathode shifts away from the anode as zinc corrosion products precipitate along concentric whitish lines that result from the location of the peak cathodic current. Sodium phosphate inhibits corrosion at the cut edge by precipitation of gel-like zinc phosphate clusters with barrier properties. Breakdown and repassivation of this layer can occur under certain conditions.