Effect of Citrate-Based Bath pH on Properties of Electrodeposited Cu–Zn Coating on an Aluminum Substrate

Abstract

In this study, Cu–Zn alloys were deposited in citrate-based electrolytes on aluminum substrate by electrodeposition method. The effect of bath pH variation on the properties of the obtained Cu–Zn alloy coatings was investigated. The electrochemical behavior of the citrate-based baths and the crystalline structure, surface morphology and elemental content, electrical resistivity and thermal behavior of the alloy coatings were analyzed. According to the results of cyclic voltammetry (CV) analysis, increasing bath pH caused a negative shift in the cathodic deposition potential. In addition, the anodic dissolution peaks first shifted to the positive side with increasing pH and then shifted back to the negative direction. According to the results of XRD analysis, the phase structure of Cu–Zn alloys generally consists of α and β′ phases, but according to differential scanning calorimeter (DSC) analysis, it is possible that there is a γ phase in the structure in addition to these phases. In addition, pH increase (4.5 to 6.5) caused a relative increase in crystal grain size (~14 to ~ 25 nm). The Zn content of Cu–Zn coatings first increased (~pct 15 to ~ pct 55) with pH increase, then followed a horizontal trend (~pct 55 to ~ pct 59) with further pH increase and then exhibited a slight decreasing trend (~pct 59 to ~ pct 52). The pH increase significantly affected the surface morphology of the coatings and denser coatings were obtained with increasing pH. While the electrical resistivity of Cu–Zn coatings first increased (0.0408 to 0.0696 µΩcm for 297 K) with increasing pH, it tended to decrease (0.0696 to 0.0479 µΩcm for 297 K) again at higher pH values. In addition, the electrical resistivity of the coatings increased with increasing measurement temperature. According to DSC analysis of the coatings, endothermic peaks were obtained, possibly representing the transformation from γ to β′ phase.

Graphical Abstract