Electrochemical Behavior of Citrate Cu-Zn Electrolytes for Copper Alloys Electrodeposition

Brass coating is ordinary produced by a successive deposition of zinc and copper, followed by a thermal diffusion step, despite its high energy consumption[1]. Direct alloy electroplating is difficult, because of the difference in reduction potentials of zinc and copper which is over than 1 V, making commercial non-cyanide baths not available. To allows a simultaneous deposition of those two cations on the cathode surface, the difference between their reduction potentials must be decreased to a value lower than 200 mV [2], by the addition of complexing agents. An experimental and theoretical study of the influence of complexing agent on the electroplating process of brass was conducted. To this end, a simulation of the chelates distribution as a function of pH and ligand concentration was done using Scilabâ software. Then, optimal speciation conditions in regards of bath stability were chosen, and the obtained aqueous citrate electrolytes were characterized by UV–VIS spectrophotometry, copper in and studies of current polarization curves for copper–zinc deposition. It appears that a 1:10 copper to citrate ratio is the most promising electrolyte. Linear sweep voltammetry presents peaks reduction for copper and zinc as well as for codeposition conditions. From this curves, various deposition potential have been chosen, and a same charge quantity was used to elaborate corresponding deposits. The latter will be quantify by anodic dissolution, giving the reaction Faradic yield.Finally, the technical feasibility of plating was made, and the possibility to control the alloy element content was checked using Hull Cell plating test. It appears that current density as well as zinc concentration are the main parameters to govern the alloy composition and properties. [1] Q. WANG, W. DU, L. LI, X. LÜ, S. ZHANG, The effect of ionic liquid additives on the electroplating brass from non-cyanide bath, Chinese Sci. Bull. (Chinese Version). 60 (2015) 2553. doi:10.1360/N972015-00317. [2] C. Meudre, L. Ricq, J.-Y. Hihn, V. Moutarlier, A. Monnin, O. Heintz, Adsorption of gelatin during electrodeposition of copper and tin–copper alloys from acid sulfate electrolyte, Surf. Coatings Technol. 252 (2014) 93–101. doi:10.1016/J.SURFCOAT.2014.04.050. [3] A. Dridi, L. Dhouibi, J.Y. Hihn, P. Berçot, W. Sassi, M. Rezrazi, Study of the influence of complexes stability on the kinetic of CuZn electroplating in a citrate bath, Submitted Electrochim. Acta. Figure 1