Acid Rain-Induced Corrosion of Sn–0.7cu–xin Solder Alloys: A Comparative Study

This study investigated the effect of minor indium additions (0.1, 0.5, 1.0 wt. %) on Sn-0.7Cu solder, resulting in Sn-0.7Cu-0.1In, Sn0.7Cu-0.5In, and Sn-0.7Cu-1.0In solders. The influence of indium addition on microstructure, melting temperature, microhardness, and corrosion resistance of the alloys was investigated. Corrosion resistance was evaluated in simulated acid rain with a pH of 3.5 using immersion and potentiodynamic polarization tests. Results indicated that the melting temperature decreased from 225.9 °C to 223.1 °C with increasing indium content. The addition of indium also refined the microstructure, reduced the β-Sn phase fraction, and improved the microhardness of the solder. Analysis of corrosion products identified SnO and SnO2, confirming that tin is the primary element susceptible to corrosion in Sn-0.7Cu-xIn solders exposed to acidic conditions. Polarization curves revealed that corrosion resistance improved significantly with increasing indium content, with the lowest corrosion rate observed at 1.0 wt. % of indium