Study of the influence of the polyalcohol sorbitol on the electrodeposition of copper–zinc films from a non-cyanide bath

The electrodeposition of copper–zinc on to AISI 1010 steel from an alkaline non-cyanide solution containing sorbitol was investigated, with various proportions of the metal ions in the bath. Voltammetric curves indicated that the complexation of copper ion by sorbitol is beneficial, since the copper complex reduction potential is close to that of the zincate ion, implying that codeposition of copper and zinc should occur. EDS analysis showed that varying the ratio of copper to zinc ions in the plating bath affects the proportion of metals in the deposits, leading to golden or greyish bright films, even in the high-hydrogen-evolution potential region, indicating that sorbitate anions prevent the deposits becoming darker in this region. The narrow variation in film colour at various deposition potentials and charge densities showed that rigorous control of the alkaline-sorbitol plating bath and deposition conditions is not necessary. SEM analysis showed that the films were without stress and the substrate was fully covered. X-ray spectra suggested that a mixture of Cu80 and CuZn2 alloy was deposited at −1.14 V in all the baths studied while Cu0.61Zn0.39 (Cu-70 bath), Cu5Zn8 (Cu-50 bath) and CuZn5(Cu-30 bath) films were deposited at both −1.45 and −1.60 V.