Effect of Curing Temperature on Corrosion Resistance of a Chromium-free Coating on Hot Dip Galvanized Steel Sheet

In this work, tannic acid powder, fluoro titanic acid solution and colloidal silica were used to prepare a coating on a hot dip galvanized steel sheet. The pH value of the passivating solution ranges between 2~7, and the curing temperature is 20 °C, 60 °C, 80 °C and 100 °C. The interface connectivity of the coating was investigated using a Fourier transform infrared spectrometer. Microstructures of the coating were observed using a field-emission scanning electron microscope equipped with an energy dispersive spectrometer and an X-ray photoelectron spectrometer. The corrosion resistance of the coating was studied using an electrochemical workstation. The results show that the coating thickness increased with increasing curing temperature. A coating thickness of 0.62 μm is achieved with a curing temperature of 100 °C; at this temperature, the corrosion potential Ecorr is 410.5 mV, and the polarization resistance (Rp) is 2.13×10 6 cm -2 ohms. These conditions provided the best corrosion resistance of the coating.