Preparation and Corrosion Resistance of Ni/Cu/Zn Multilayer Coating

Ni/Cu/Zn multilayer coating was prepared on low carbon steel substrate by electrodeposition. The microstructure of the Ni/Cu/Zn multilayer coating was observed by scanning electron microscopy (SEM). The corrosion resistance of the Ni/Cu/Zn multilayer coating was evaluated by the brine immersion testing in which NaCl mass fraction was 5%. The electrochemical properties of Ni/Cu/Zn multilayer coating in 5.0% (mass) NaCl solution were measured by electrochemical impedance spectroscopy (EIS) technique. The results show that:the particles in the under layer of nickel were stacked interlacedly as four pyramid type, the particles in the middle layer of copper were deposited by round cell structure, and the surface layer of zinc was flat and compact without apparent pores. The Ni/Cu/Zn multilayer coating exhibited good corrosion resistance, showing a value of electrochemical impedance of 5 623 Ω·cm². The immersion time of red rust spot occurring on the coating surface in brine reached 2 880 h which was 5-8 times of that for single layer coating with the same thickness.