Improvement in the mechanical properties of eutectic Sn58Bi alloy by 0.5 and 1 wt% Zn addition before and after thermal aging

Abstract A comparative analysis of the microstructure and the mechanical properties of the eutectic Sn58Bi, 0.5 wt% and 1 wt% zinc (Zn)-functionalized Sn58Bi alloys was conducted before and after solid-state thermal aging. Cross-sectional microstructure observation and tensile tests were performed on bulk solder alloys. The fracture surfaces were observed after the tensile tests. In addition, the mechanical properties of individual Sn and Bi phases were obtained using nanoindentation tests. The results indicated that finer microstructures were obtained in the Zn-added samples compared to the eutectic Sn58Bi before and after aging since the Sn–Bi phase boundary segregation of Zn occurred during aging, and the movement of the diffusion entities (Sn and Bi atoms) through the boundaries was obstructed. The fine microstructure was responsible for the ultimate tensile strength improvement obtained in the Zn-added samples. Meanwhile, a significant hardness decrease of the Sn phase in the Sn58Bi1Zn alloy was believed to be a possible reason for the superior elongation of the Zn-added samples.