A resistance-wire type strain gauge assembly affixed to the reverse side of a copper plating substrate was used to measure the real-time variation in the internal strain developed during the deposition and dissolution of zinc-cobalt alloy films by single cycle voltammetric sweeping. An internal tensile strain developed during the cobalt deposition that began near −0.65V (vs. Ag/AgCl sat. KCl). However, in the potential region of −0.85V to −0.98V, the tensile strain stagnated due to the suppression of the cobalt deposition caused by the adsorption of zinc hydroxide produced on the electrode. On the other hand, in the potential region of −0.98V to −1.06V, the tensile strain again increased due to the cobalt deposition occurred with the onset of the electrochemical reduction of zinc ions. However, in the subsequent more negative potential region of −1.06V to −1.20V, the internal strain changed from tensile to compressive with the formation of a zinc-rich γ-phase of the Co-Zn alloy.
After the electrode potential was reversed at −1.20V, the compressive strain was maintained by the alloy deposition in the potential region of −0.98V to −1.20V. However, with the cessation of the electrochemical reduction of zinc ions in the potential region more noble than −0.98V, the strain changed from compressive to tensile with selective electrolytic-leaching of zinc from the alloy deposits.