Electrochemical corrosion behaviour of Pb-free Sn–8.5Zn–0.05Al–XGa and Sn–3Ag–0.5Cu alloys in chloride containing aqueous solution

The electrochemical corrosion behaviour of Pb-free Sn–8.5Zn–0.05Al–XGa and Sn–3Ag–0.5Cu alloys was investigated in 3.5% NaCl solution by using potentiodynamic polarization techniques. The results obtained from polarization studies revealed that there was a negative shift in the corrosion potential with increase in Ga content from 0.02 to 0.2 wt% in the Sn–8.5Zn–0.05Al–XGa alloy. These changes were also reflected in the corrosion current density (Icorr) value, corrosion rate and linear polarization resistance (LPR) of the four element alloy. However, for Sn–3Ag–0.5Cu alloy a significant increase in the corrosion rate and corrosion current density was observed as compared to the four element alloys. SIMS depth profile results established that ZnO present on the outer surface of Sn–8.5Zn–0.05Al–0.05Ga alloy played a major role in the formation of the oxide film. Oxides of Sn, Al and Ga contributed a little towards the formation of film on the outer surface of the alloy. On the other hand, Ag2O was primarily responsible for the formation of the oxide film on the outer surface of Sn–3Ag–0.5Cu alloy.