Effects of composition and reflowing on the corrosion behavior of Sn-Zn deposits in brine media

Tin-zinc deposits with the Zn content varying from 13 to 0 weight percents (wt%) (close to the eutectic point of the Sn-Zn alloy, Sn-9Zn) were electroplated onto iron-coated copper substrates from a near-neutral (pH 5.0), non-cyanide bath. The corrosion parameters, including open-circuit potential-time curves (E_OCP-t), corrosion potentials (E_CORR), and corrosion currents (i_CORR), of this series of materials before and after reflowing in N₂ at 250 °C for 10 min were determined and systemically compared in a brine medium containing 3 wt% NaCl. For the as-prepared deposits, the Sn-5Zn deposit showed an activity very close to but more active than that of Fe in this brine medium. This deposit also exhibited the highest corrosion resistance in the study of electrochemical impedance spectroscopy (EIS). For the reflowed deposits, the anticorrosive ability of Sn-Zn deposits with the Zn content <9 wt% became relatively poorer than that of their corresponding as-prepared counterparts while the Sn-9Zn and Sn-5Zn deposits with reflowing showed the best anticorrosive properties in the 3 wt% NaCl solution. The crystalline information and the surface morphologies of the deposits before and after the reflowing treatment were compared by means of the X-ray diffraction (XRD) and scanning electron microscopic (SEM) analyses.