The Effect of Electrophosphating Time on Zn-Ni Phosphate Coating Properties

In this study, Zinc-Nickel electrophosphate coating was applied on galvanized steel. microstructure, corrosion resistance and porosity of coating were characterized using scanning electron microscopy, polarization test and electrochemical method respectively, Zn-Ni electrophosphate coating was applied on galvanized steel substrate using cathodic electrochemical method at different operation times, the result of this study indicated that, by using cathodic electrochemical method, coating with the desired properties can be obtained at low temperature bath. Result of microscopic study indicated that, in low operation time, the surface of the substrate not fully covered by phosphate crystals, consequently, coating with poor corrosion resistance can be obtained, also at the high operation time, excessive growth of phosphate crystals leads to high porosity in the coating. Therefore, by increasing the operation time from ۲۰ min to ۴۰ min the corrosion current density increase from ۰.۶۸µA/cm۲ to ۲.۵۴ ۶۸µA/ cm۲ consequently, the optimized time for obtaining the coating with desired properties is ۲۰ minutes. Also the deposition mechanism of Zn-Ni electrophosphate coating was investigated in this study.

کلیدواژه ها:

Electrophosphating ، Zn-Ni phosphating ، Corrosion resistance ، Galvanized steel ، الکتروفسفاته کاری ، فسفاته کاری دوکاتیونی روی-نیکل ، مقاومت به خوردگی ، فولاد گالوانیزه