Microstructure evolution and tensile creep behavior of Sn–0.7Cu lead-free solder reinforced with ZnO nanoparticles

This paper presents the influence of aging temperature as well as ZnO nanoparticles addition on the properties of Sn–0.7Cu solder. A series of Sn–0.7Cu–ZnO composite solders with ZnO nanoparticles traces (0, 0.1, 0.25, 0.5 and 1.0 wt%) has been fabricated. After being solution heat treated at 443 K for 2 h, specimens were cooled at 273 K by water quenching. All the specimens were isochronally aged for 2 h at temperatures up to 423 K. Subsequently, all samples were quenched into iced water at 273 K. The microstructure evolution, the tensile creep properties and the thermal behavior of the new fabricated solder alloys were studied. Differential scanning calorimetry measurements indicated that the ZnO nanoparticles addition increases slightly the melting point of the investigated composite solders within the range of 227.7–229.2 °C with less than 1.6 °C temperature difference. Microstructural evolutions revealed the efficient refinement of the Cu₆Sn₅ and Cu₁₀Sn₃ intermetallic compounds by the addition of ZnO nanoparticles. Tensile creep tests showed that the creep rate at the steady state stage increases with increasing both the aging temperature and the applied stress. The improvement of the solders creep resistance has been achieved by the increasing of the nanoparticles content up to 0.25 wt%. The deficiency of the creep resistance occurred with the excessive addition of ZnO particles. The mean values of the stress exponents and activation energies indicated that the steady state creep stage is controlled by dislocation-pipe diffusion in the tin matrix as the dominant operating mechanism.