Effect of Ti addition on the electrochemical behaviour of Sn-0.7Cu-xTi lead-free solders alloys in 3.5 wt.% NaCl solution

The electrochemical corrosion behaviour of Sn-0.7Cu-xTi (x = 0, 1, 2, and 3 wt.%) lead-free solder alloys was investigated using Potentiodynamic polarisation analysis in a 3.5 wt.% sodium chloride solution at room temperature. This study aims to determine the impact of titanium (Ti) variation on the corrosion properties of Sn-0.7Cu-xTi alloys and to provide insights into the optimal composition of Sn-0.7Cu solders based on their corrosion resistance. According to electrochemical impedance spectroscopy (EIS) data, the addition of Ti influenced the corrosion product surface, altering the electrochemical behaviour from charge transfer control to diffusion control. Notably, the inclusion of a trace amount of Ti (1 wt.%) significantly enhanced the corrosion resistance and microstructure of Sn-0.7Cu solder, as evidenced by a markedly higher total resistance (R_t) and a substantially lower corrosion current density (I_corr). However, the excessive addition of Ti (Ti > 1 wt.%) led to the formation of Ti₂Sn₃ intermetallic compounds (IMCs), which diminished the corrosion resistance of Sn-0.7Cu-xTi solders. The primary corrosion products identified were Sn₃O(OH)₂Cl₂ with minor amount of TiO₂, SnO₂ and SnCl₂ complexes. This study concludes that an optimal Ti content of 1 wt.% in Sn-0.7Cu solder significantly improves corrosion resistance, while higher Ti levels adversely affect the alloy's performance.