Potassium salt based alkaline bath for deposition of Zn–Fe alloys

A new alkaline bath was proposed based on highly concentrated potassium hydroxide for electrodeposition of Zn–Fe alloys. Triethanolamine was used as the complexing agent to eliminate precipitation of ferrous hydroxide and to enable the co-deposition of Zn and Fe. The conductivity value of the proposed baths is 161–188% higher than that of a known formula. From cathodic linear sweep voltammograms the co-deposition of Zn and Fe in the proposed bath is applicable. Zn–Fe alloys with different compositions were achievable by tuning the deposition variables such as the ion ratio Zn/Fe and the deposition current density. The co-deposition of Zn and Fe is an anomalous type under a small current density and switches to the regular one under a larger current density. The transition current density was found to be 0.075 and 0.05 A cm−2 for Baths 1 (ion ratio Zn/Fe=13) and 2 (Zn/Fe=25), respectively. A mechanism based on adsorbed Fe-TEA barrier-layer was proposed to explain this transition. There is a more than 40% enhancement in cathodic current efficiency by using the proposed Bath 2 versus the known formula. Comparing with Zn coating, the deposited Zn–Fe layer reveals 10% nobler corrosion potential, −0.987 vs. −0.897 VSCE, and two times smaller corrosion current density, 42.0 vs. 19.7 μA cm−2. The proposed baths are much easier for bath control during deposition.