The effect of alloying element gallium on the polarization characteristics of Pb-free Sn-Zn-Ag-Al-XGa solders in NaCl solution

The polarization characteristics of Sn-8.5Zn-0.5Ag-0.1Al-XGa lead-free solders were investigated in 3.5% NaCl solution where X ranges from 0.05-1.5 wt%. The results show that Ga affects the anodic polarization behaviour of the solders. Passivation behaviour is observed for all the investigated Sn-8.5Zn-0.5Ag-0.1Al-XGa solders. Increase in the Ga content from 0.05 to 0.25 wt% increases the ability for passivation but the oxide film formed due to passivity is not so protective. However Ga content > 0.25 wt% enhances corrosion and decreases the protective power of the passive film. The magnitude of the passivation current densities depend on the composition of the solders and the potentials applied. Layers of oxides of tin and zinc are responsible for the passivation behaviour. XRD and SEM results revealed the formation of corrosion products like SnO, ZnO, SnO₂ at different potentials during the polarization study.