CuZn Electrodeposition in Cyanide-Free Electrolytes: Influence of Citrate/Metal ratio and pH on Simultaneous Copper and Zinc Reduction Kinetics and Alloy Composition Control

Abstract

An experimental and theoretical study of CuZn electroplating mechanisms is conducted in trisodium citrate baths. The study aims to evaluate the influence of different bath parameters: ligand concentration, pH, metal complexation behaviors and solution ionic strength on bath stability and, if applicable, co-reduction processes. UV–VIS spectrophotometry, studies of current polarization curves for copper–zinc deposition, and speciation diagrams of copper in aqueous citrate solutions are incorporated to review the role of the blocking agent and pH on co-reduction ability issues. The CuZn electroplating process is also investigated using LSV curves in different baths, while focus is placed on the rate of metal ion diffusion to the growing centers. Following which, an optimized bath, based on control of the species of the blocking intermediates, is selected and investigated to check CuZn reduction potential rapprochement. Finally, deposition behaviors of copper, zinc and both combined are investigated to correlate deposition kinetics and efficiency to deposit properties (thickness/element content). Chronocoulometric curves of different CuZn deposits combined with their deconvoluted potentiodynamic dissolution peaks are used. Hull cell tests are performed to evaluate current control on a large range of CuZn coatings. Deposit properties are studied using X-ray fluorescence spectrometry.