Production of low-Sn Cu-Sn alloy coatings onto steel substrate using sodium citrate bath – part 1: the effect of current mode (DC or SPC) and applied current on the chemical, morphological, and anticorrosive properties of the coatings

This work reports the production of low-tin Cu-Sn alloy coatings on carbon steel substrates using a bath containing CuCl₂, SnCl₂ , and sodium citrate. In the first part of this study, the coatings were electrodeposited by direct and simple pulse current processes (DC and SPC, respectively). Different current density values were used, while the pulse frequency and duty cycle remained constant. Independent of the current mode used, low-tin Cu-Sn coatings, showing globular surface morphology and Cu₆Sn₅ as the main compositional phase, were produced. Both the current mode and the applied current density affected the anticorrosive properties of the coatings. The most protective DC and SPC coatings, showing Sn content < 3 wt.% and compact morphology, were prepared using j = 80 A m^-2 and j_c = 167 A m^-2, respectively. High charge transfer resistance values were verified even after immersion for 24 h in 0.5 mol L^-1 NaCl solution. (author)