Electrochemical Deposition of γ-Phase Zinc-Nickel Alloys from Alkaline Solution

Zinc-nickel alloys with 8-15% nickel were deposited onto stainless steel for corrosion protection. Alkaline deposition conditions were utilized given that alkaline systems have been found to offer superior substrate coverage which results in better corrosion protection of the metal substrate (stainless steel) compared to acid bath depositions. This method utilizes ammonium hydroxide as the base source with a working pH range of 9-9.5. Sodium acetate was used as the complexing ligand as it was found to stabilize the metal ions in the electrolytic solution. Strongly adhering, quality deposits were obtained with electrodeposition at room temperature. Bath compositions and applied potential had an effect on morphology of the films as seen in scanning electron microscopy. Upon examination by x-ray diffraction and atomic absorption spectroscopy, all deposits were confirmed as γ phase zinc-nickel alloys with a nickel content of 8-15%. The corrosion potential for the γ-phase coatings was improved over the pure zinc coatings.