Electrochemical Corrosion Resistance Evaluation of Zn-Ni Alloy Electroplating Process in Zincate Bath

Zn-Ni alloy plating, has been adopted as a plating technology to address the drawbacks of pure Zn plating while increasing the corrosion resistance. This study conducted Zn-Ni alloy electrodeposition using a zincate bath by varying the Zn/Ni molar ratios and process conditions. The Ni content in the alloy layer was analyzed using energy-dispersive X-ray analysis to investigate the changes in the eutectoid ratio. Additionally, a trivalent chromate solution was prepared as a post-treatment technique to assess the changes in the corrosion resistance over different treatment durations. Furthermore, an electrochemical behavior analysis was conducted using the Tafel technique, measuring parameters, such as corrosion potential (Ecorr) and corrosion current densities (icorr) in a 3.5 wt% NaCl solution. The corrosion rate measured in mils penetration per year was calculated by data fitting. Scanning electron microscopy analysis was used to examine the surface morphology of the electrodeposited Zn-Ni alloy. The crystal structure of the electrodeposited layer was characterized using X-ray diffraction. The analysis results confirmed the formation of a single gamma-Ni5Zn21 phase, known for its outstanding corrosion resistance. A composition of 17.2 wt% Ni was achieved when the ZnO concentration was 0.10 M and the NiCl2 concentration was 0.01 M, providing optimal corrosion resistance. The Zn-Ni alloy electrodeposition layer exhibited an Ecorr of -1.0 V or lower. Following the trivalent chromate treatment, a potential increase of approximately +200 mV was observed. Furthermore, the icorr at the icorr potential, ranging from log10-2 to log10-4 A/dm2, decreased.