Electrochemical and XRD studies of Cu–Zn coatings electrodeposited in solution with d-mannitol

Studies of the phase and chemical compositions as well as of the surface morphology of Cu–Zn alloys electrodeposited in the alkaline solution containing d-mannitol were carried out using the voltammetric, XRD, EDX and SEM techniques. The prime objective of the studies was to refine the phase composition of the electrodeposited Cu–Zn alloys. The studies revealed that at potentials more positive than that of the reversible Zn2+/Zn electrode good appearance yellow Cu–Zn coatings containing up to ∼40 at.% of Zn can be deposited. It was established that at potentials mentioned more than half of the total Zn quantity was incorporated into the deposit as Zn(OH)2 and only the rest was in the α phase of Cu–Zn alloy. At potentials negative to that of the reversible Zn2+/Zn electrode the proportion of Zn in the deposit increased abruptly up to 60–70 at.% and Zn(OH)2 was not detected. The phase composition of the Cu–Zn deposits as a function of the proportion of Zn in the deposit presented the same consequence of phases as that in the equilibrium phase diagram. The only difference was that the zinc-rich phases were formed in the deposits with a lower proportion of Zn as compared to that according to the equilibrium phase diagram. The studies carried out imply that morphology of the deposit and interdiffusion of Cu and Zn is very important for the phase composition of the electrodeposited Cu–Zn alloy.