The effects of S addition on the corrosion behaviour of Sn-9Zn solders in 3.5 wt-% NaCl solution were investigated using dynamic potential polarisation, electrochemical impedance spectroscopy techniques and weight loss measurement. The results indicate that S addition could obviously improve the corrosion resistance of Sn-9Zn solder alloy as revealed by much lower corrosion current density, higher impedance and the reduced weight loss. It is believed that the homogeneous microstructures of Sn-9Zn, especially the black refined Zn-rich phases are favourable to improve its corrosion resistance. SEM observations found that S addition might promote the formation of denser and more uniform corrosion products on the solder surface. The main corrosion product was Zn5(OH)8Cl2·H2O determined by EDS and XRD analysis.

Incorporation of Bi into Sn-0.7Cu-0.08S lead-free solder alloy was applied to investigate its advantages on the melting temperature, wettability, microstructure, mechanical properties and corrosion behaviour. The results indicate that the addition of Bi lowers the melting temperature of the Sn-0.7Cu-0.08S, but enlarges its pasty range. The wettability of Sn-0.7Cu-0.08S on Cu substrate is considerably enhanced with the increase of Bi, as well as the ultimate tensile strength and vickers hardness. The improvement of the mechanical properties can be attributed to the refined microstructure by Bi addition. The corrosion resistance of Sn-0.7Cu-0.08S is obviously increased with the increase of Bi content. Analyses by SEM and XRD indicate that the corrosion product on the solder alloy surface is SnO2.