Electrodeposition of CuZn films from free-of-cyanide alkaline baths containing EDTA as complexing agent

• Solutions free-of-cyanide for Cu–Zn electrodeposition were developed.
• EDTA was the complexing agent employed alternatively to cyanide.
• Continuous CuZn coatings, free of cracks, could be obtained.
• Bright golden CuZn coatings and high efficiencies were obtained at low current densities.
• EDTA has prospects to substitute cyanide in CuZn electrodeposition.

In order to study alternative complexing agents for cyanide in Cu–Zn electrodeposition, electrodeposits from cyanide-free alkaline baths containing EDTA as complexing agent were analyzed. The electrodeposition was carried out under constant current conditions (galvanostatic) on AISI 1010 steel substrates. Electrodeposition process and the deposits were characterized with surface morphological analyses, stripping anodic voltammetries, chemical composition and X-ray diffraction (XRD) analysis. Current efficiencies (CEs) higher than 90% for Cu–Zn electrodeposition were obtained at low deposition current densities (jdep) for baths with the highest molar [Cu2 +]/[Zn2 +] ratio in solution (70/30). For higher jdep, smaller CEs were obtained. By scanning electron microscopy, fine-grained deposits were observed at jdep of − 4.0 and − 10.0 mA cm− 2 for deposition charge densities (qdep) of 2 and 10 C cm− 2 and for jdep of − 20 mA cm− 2 only for 2 C cm− 2 in the analyzed range of jdep and qdep. Continuous deposits free of cracks were obtained. Colors of deposits such as: bright golden and dark brown could be obtained, depending on jdep and qdep. Burning of deposits was observed at jdep of − 80 mA cm− 2 at high qdep. Semi-quantitative chemical analyses of deposits from Cu70Zn30 baths indicated richer in copper deposits. By XRD analysis CuZn2, Cu0.61Zn0.39, Cu and CuO were detected and no inclusions of ZnO. EDTA has prospects for substituting cyanide, however in a limited range of jdep and qdep.