Verification of Deposition Mechanism of Zinc Alloys Using Non-aqueous Plating Solutions

Electrodeposition of Zn alloys with iron-group metals, Cr and Mn was conducted in non-aqueous solutions such as methanol and N, Ndimethlyfromamide and the alloy deposition behavior was compared with that in aqueous sulfate solutions. The results obtained are described as follows: 1) The electrodeposition behavior of Zn-iron-group metals and Zn-Cr alloys, in which the formation of Zn hydroxide due to pH rise in the cathode layer plays an important role during the codeposition process in aqueous solutions, was quite different between the non-aqueous and aqueous solutions. 2) The deposition of Zn-iron-group-metal alloys in the non-aqueous solutions showed the typical feature of normal type codeposition, in which electrochemically more noble iron-group metal deposits preferentially over most plating conditions. 3) In the codeposition of Zn with Cr, the deposits of about 90 mass% Cr was obtained in the non-aqueous solutions containing 80-90mol% of Cr3+, while the maximum Cr content was about 40 mass% in aqueous solutions. 4) Since Zn hydroxide was not involved in the codeposition of Zn with Mn in aqueous solution, the deposition behavior of Zn-Mn alloy in the non-aqueous solutions was almost the same as that in aqueous solution.