Influence of alloying elements on microstructure, mechanical properties and corrosion behaviour of hypoeutectic Sn-6.5wt%Zn-0.5 wt%X (X = Ag, Al, Cu) lead-free solders

Lead-free solders are promising candidates for the replacement of Sn–Pb solders due to their environmental friendly, good thermal properties and wettability which render them suitable for this application. In this study, a set of lead-free solders Sn-6.5 wt. and Sn-6.5 wt% Zn-0.5 wt% X (X = Ag, Al, Cu) were studied by metallography, mechanical and electrochemical techniques. The results show that the addition of the alloying elements Ag, Al and Cu modifies the amount of the eutectic phase and promotes the formation of intermetallic compounds (IMCs). The corrosion resistance of the samples also modified, showing that the formation of IMCs can have detrimental effects with higher current densities in saline media, as determined for the Ag and Al alloyed solders. The corrosion resistance is higher for the unalloyed and the Sn-6.5 wt%Zn-0.5 wt% Cu alloy. However, the addition of Cu not only stabilizes the corrosion products thus increasing the protective properties of the alloy, but also modifies the mechanical behaviour of the lead-free solders and so enhancing the UTS values and ductility. Furthermore, the surface morphology is influenced by the alloying elements showing a smooth surface (Sn-Zn, Cu) or a highly corroded appearance with round aggregates (Ag and Al). These new lead-free solders have a lower melting point with higher ductility than the commercial SAC 305. Therefore, these alternatives have high potential in applications in mechanical engineering.