Zn-Ni Electrophosphating on galvanized steel using cathodic and anodic electrochemical methods

Electrophosphating is the novel method for accelerating the low temperature phosphating bath. This method can be performed as cathodic and anodic treatments. Both of them influence the coating deposition mechanism and therefore coating properties. In this study Zn-Ni electrophosphate coating was applied on galvanized steel using cathodic and anodic electrochemical methods. Microstructure, composition and corrosion resistance of coating were characterized by using a scanning electron microscopy, X-ray diffraction method and potentiodynamic polarization test respectively. The results of this study indicated that, by using cathodic method, compact phosphate coating with high corrosion resistance can be obtained. The result of X-ray diffraction pattern indicated the presence of Zn and Ni along with zinc and nickel phosphate in the phosphate layer. It is indicated that the phosphate crystal shape of cathodically coating was flower and plate like and only flower like crystals are formed in anodically coating. Also results indicated that, the phosphate coating obtained by anodic electrochemical method has high porosity and consequently poor corrosion resistance. Also, based on the study results, applications proposed for coatings that obtained by cathodic and anodic electrochemical methods.