Preparation and Characterization of Cr-free passivation films on zinc coating using Response Surface Methodology and Electrochemical Methods

Response surface methodology (RSM) was used in this study to determine the optimum operating conditions for the reduction of galvanized sheet corrosion using a Cr-free passivation films. Passivation films layer with strong corrosion resistance was formed on the surface of galvanizing which was impregnated in chromium-free passivating agent. Furthermore, the RSM was used to ascertain the main and interactive effects (deviation between the experimental and theoretical values: 0.12%). The coefficient of determination (R 2 ) showed that the RSM approach was appropriate for optimization of the Cr-free passivator. Silane coupling agent, ammonium molybdate, nanosilica, and tannic acid played a key role in changing the corrosion area and potential. The results revealed that, compared with Cr 6+ passivation, Cr-free passivation yielded considerably more homogeneous and smoother surfaces (surface roughness of Cr-free passivation film: 0.54 μm). In addition, the properties of the zinc coating after Cr- free passivation were clearly superior to those of the zinc coating subjected to the conventional Cr 6+ passivation treatment. E corr, current density, and polarization resistance values of this superior coating were -1073 mV, 0.017 A cm -2 , and 989.2 Q, respectively. This study can serve as an experimental and a theoretical guide for the development of Cr-free passivation films.