Microstructure and tensile behavior of Sn–5Sb lead-free solder alloy containing Bi and Cu

Tensile deformation behavior of Sn–5Sb, Sn–5Sb–1.5Bi, and Sn–5Sb–1.5Cu alloys was investigated at temperatures ranging from 298 to 400 K, and strain rates ranging from 5 × 10−4 to 1 × 10−2 s−1. Addition of Bi and Cu into the binary alloy resulted in an increase in both ultimate tensile strength (UTS) and ductility. The improved strength of the Bi-containing alloy can be attributed to the microstructural refinement, uniform distribution of the SnSb intermetallic particles, and solid-solution hardening effect of bismuth in the β-Sn matrix. The enhanced strength of the Cu-containing alloy was ascribed to the presence of the Cu6Sn5 intermetallic particles and structural refinement. The ductility of both ternary alloys was, however, improved by the structural refinement, caused by the addition of alloying elements. The results of tensile tests indicate that the strength of all three alloys increase with increasing strain rate and decrease with testing temperature. The variation of ductility with strain rate showed a descending trend, while it exhibited a minimum at medium testing temperatures. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in Sn–5Sb is dislocation climb over the whole temperature range investigated. For the ternary alloys, however, grain boundary diffusion and dislocation climb are the deformation mechanisms at high and low temperatures, respectively.

► Enhanced strength of Sn–5Sb–1.5Bi was due to solid solution hardening of Bi in Sn.
► Enhanced strength of Sn–5Sb–1.5Cu was due to formation of Cu6Sn5 particles.
► Improved ductility was due to structural refinement cased by alloying elements.
► The strength increased and the ductility decreased with increasing strain rate.
► The strength decreased and the ductility increased with increasing temperature.