Corrosion Protection of Electro-Galvanized Steel by Green Conversion Coatings

A cerium-based chemical conversion process was studied. First, zinc coating obtained from a free-cyanide alkaline bath, with derivative of imidazol with new brightener, was investigated, zinc-plated steel specimens were treated with a solution of 50 mmol · L−1 Ce(NO3)3. The corrosion behavior of bare and treated mild galvanized steel was evaluated during exposure to 0.5 mol · L−1 NaCl for different immersion time, using Tafel polarization curves and electrochemical impedance spectroscopy (EIS) measurements. The surface morphology of the coating was studied using scanning electron microscopy (SEM). The composition and chemical percent of the coating were examined by X-ray dispersion energy (EDAX). The results of these measurements showed that the newly developed cerium-based conversion coating process was a promising candidate for replacing the conventional chromate treatments used at present for galvanized steel.