Influence of Pulse Parameters on a b Cuzn Alloys Electrodeposited Coatings

Abstract

Cu-Zn alloys is the most manufactured copper alloy in the word since it offers a wide range of properties depending on its zinc content. Although brass plating has been studied since 1841 by Ruoltz, and despite several studies devoted process improvement, CuZn coatings from non-cyanide baths shows low reproducibility, poor adhesion, inhomogeneous color and frequently cannot be deposited directly on steel. These problems are mainly attributed to an unusual crystalline phase distribution[1] [2]. Therefore, to obtain a higher quality of metallic electrodeposited alloy, it is mandatory to control the activity of the nobler ion in the solution, which is much more likely to be reduce. To that end, copper and zinc reduction potentials have to be bring closer by the use of a complexing agent of the copper ions. An electrolyte with a low citrate concentration has been developed and its electrochemical behavior extensively studied [3]. Varying Citrate concentrations will influence zinc electrodeposition and bath stability, giving the hand of the control of alloy element content. For the optimum conditions, CuZn coatings were obtained in a large range of Zn content (from 11% to 100%) as a function of Zn concentration and current density. Crystalline structures of the α β brass deposits were then identified in the range of 35% to 45% in Zn content, in order to be compared to commercial cast brass. The present study discusses the effect of pulse current for a selection of electrolytes, at the optimum of copper and citrate concentration. Wave modulation is investigated in order to compare Zn content and phase distribution for the same average current density. A particular focus was made on the quantification by XRD phase determination and its comparison with anodic dissolution. The best conditions have been tested on larger samples, to check adherence, homogeneity and to try to reach a maximum coating thickness and the right physical aspect than for the cast brass alloys. [1] J.C. Ballesteros, L.M. Torres-Martínez, I. Juárez-Ramírez, G. Trejo, Y. Meas, Study of the electrochemical co-reduction of Cu2+ and Zn2+ ions from an alkaline non-cyanide solution containing glycine, J. Electroanal. Chem. 727 (2014) 104–112. doi:10.1016/J.JELECHEM.2014.04.020. [2] T. Vagramyan, J.S.L. Leach, J.R. Moon, On the problems of electrodepositing brass from non-cyanide electrolytes, Electrochim. Acta. 24 (1979) 231–236. doi:10.1016/0013-4686(79)80030-4. [3] A. Dridi, L. Dhouibi, J.Y. Hihn, P. Berçot, W. Sassi, E.M. Rezrazi, Study of the influence of complexes stability on the kinetic of CuZn electroplating in a citrate bath, Submitted Electrochim. Acta. Figure 1