Investigation of microstructure and mechanical properties of novel Sn–0.5Ag–0.7Cu solders containing small amount of Ni

• This work investigates the effect of (0.05–0.1 wt.%) Ni additions on the SAC (0507) solder.
• Enhanced strength of SAC (0507)–0.05Ni was due to microstructural refinement and uniform distribution of the IMCs.
• Improved ductility and worsen mechanical properties of SAC (0507)–0.1Ni alloy were due to the presence of large β-Sn grains.
• Both YS and UTS increased with and decreasing temperature and decreasing strain rate.

This work investigates the effects of small additions (0.05 and 0.1 wt.%) of Ni on the microstructure and mechanical properties of low Ag content Sn–0.5Ag–0.7Cu (SAC (0507)) lead-free solder alloy. The addition of 0.05Ni resulted in the microstructural refinement, uniform distribution of the Ag3Sn and (Cu, Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. This apparently enhances the mechanical strength and microhardness. However, the addition of 0.1Ni leads to the formation of relatively high fraction of the primary β-Sn phase and the IMCs appeared abrasive within the matrix. As a result, the SAC (0507)–0.1Ni solder exhibits low tensile strength, microhardness and large elongation, which produce a soft and highly compliant bulk solder. In addition, the strength of all studied alloys increases with increasing strain rate and decreasing testing temperature, showing strong strain rate and temperature dependence. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.