Improvements in mechanical properties of Sn–Bi alloys with addition of Zn and In

Highlights: • The addition of Zn and In in a trace amount was effective in suppressing the microstructural coarsening of Sn–Bi alloys during thermal aging. Moreover, the addition of In had a significant effect on the elongation of the alloys. • The segregation of Zn at the Sn/Bi phase boundary and the formation of a solid solution of In in the Sn phase are responsible for the phenomenon of microstructural retention during thermal aging. In order to improve the mechanical properties after thermal aging of an Sn–45Bi–2.6Zn (SBZ) alloy, which we had proposed in a previous study, in this study, we prepared Sn–Bi–Zn–In alloys and investigated the effects of the addition of In and Zn on their microstructure and mechanical properties before and after thermal aging. We found that the addition of In suppressed the microstructural coarsening of SBZ during thermal aging and can potentially help reduce the brittleness of Sn–Bi alloys. Moreover, the addition of In had significant effect on the elongation of SBZ. We theorized that the segregation of Zn at the Sn/Bi phase boundary and the formation of a solid solution of In in the Sn phase are responsible for this result. Thus, the investigated alloys have potential for use as lead-free solder materials in the electronics industry.