Effect of treatment time and temperature on microstructure and corrosion behavior of Zn-Ni electrophosphate coating

In this study, the effect of phosphating time and temperature on microstructure and corrosion behavior of Zn-Ni electrophosphate coating with a galvanized steel as a substrate, were investigated. SEM and X-ray diffraction methods were used for investigation the microstructure and phase analysis, respectively. And immersion test, potentiodynamic polarization test, and Electrochemical Impedance Spectroscopy tests were used for the study of corrosion behavior. The results of this study indicated that the best coating morphology is obtained in the range between 20 and 30 min and 40-50° C. Moreover, results of corrosion studies showed that the corrosion mechanism is under diffusion control due to the formation of zinc base corrosion products.