Tin-zinc alloy electrodeposition from aqueous citrate baths

The process of tin-zinc alloy electrodeposition from aqueous citrate electrolytes was studied. The influence of applied potential, current density, hydrodynamic conditions, electrolyte composition and charge transfer on the electrodeposition of Sn-Zn alloy was determined. Depending on these parameters, coatings with different compositions and appearances can be obtained. The surface composition of deposits was ascertained by chemical analysis (WDXRF). The morphology of coatings was studied by SEM. The electrodeposition of bright, shiny Sn-Zn coatings on steel is possible from the citrate baths studied. The presence of zinc ions in the electrolyte results in a significant inhibition of tin reduction rate, which enables the electrodeposition of tin-zinc alloy layers containing from about 0.5 to 75 wt.% of Zn, with high current efficiency, within the range from 80% to almost 100%. Two phases are formed in deposits: a hexagonal zinc phase and a tetragonal β-tin phase.