Copper-rich copper–zinc alloy coatings prepared by electrodeposition from glutamate complex electrolyte: current efficiency, Tafel kinetics and throwing power

Copper-rich Cu–Zn alloy coatings were successfully codeposited on steel substrates using glutamate-based electrolytes at room temperature. The effect of various proportions of Cu2+ and Zn2+ ions in the electrolyte on the current efficiency and on the metal content in deposited alloy was studied. It was found that the current efficiency was 53–99%, depending on the operating conditions and the bath composition, which could be considered high, in comparison with those of cyanide (75%) and citrate baths (70–80%). On the other hand, the Cu content in the deposit ranged from 20% to 98%. The electrochemical kinetic data confirm that addition of monosodium glutamate (MSG) to the plating bath increases io and decreases the Tafel slope while the transfer coefficient is invariant. The relative invariance of αc, observed for increasing glutamate ion concentrations, suggests that the Cu–Zn alloy electrodeposition pathway is not affected by the presence of glutamate. The data of throwing power, throwing index and Wagner number are consistent with each other.