Live-current electrodeposition of Nickel on Zinc from modified Watt's bath

The zinc-nickel alloy coating has a better combination of corrosion and wear resistance compared to galvanised steel. Electrodeposition of multilayer zinc-nickel alloy coating on steel is an important industrial process. However, in the case of multilayer deposition, the plating of nickel over the zinc layer has an inherent problem owing to the corrosion of zinc in the conventional acidic nickel electrolytes. Conventionally a copper strike layer is introduced over zinc followed by nickel electroplating. The present work aims at understanding the effect of both Ni2+ ion concentration and live currents on the feasibility and quality of Ni deposition on Zn from a modified Watt's bath such that nickel can be directly deposited on zinc without a copper strike layer. The coating appearance, thickness and roughness are found to be strongly dependent on nickel-iron concentration and the extent of live current which prevent Zn corrosion by offering cathodic protection while simultaneously depositing nickel on zinc.