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The effects of Zn addition on microstructure development and tensile properties of Sn–2.0Ag–0.7Cu (SAC207) lead-free solders were investigated. Microstructural analysis reveal that 1.5 wt.% Zn addition not only refined the Ag 3 Sn and Cu 6 Sn 5 particles, but also increased the eutectic area and promoted the formation of small γ-(Cu, Ag) 5 Zn 8 intermetallic compound (IMC), which in turn increased the yield strength (YS), ultimate tensile strength (UTS) and Young's modulus, but the ductility decreased. With increasing Zn content up to 3.0 wt.%, the reaction phase grain, γ-(Cu, Ag) 5 Zn 8 , becomes larger and its morphology changes from a strip-like shape into flower-like or dendritic shape. Moreover, the Ag 3 Sn and Cu 6 Sn 5 particles are significantly diminished. The observed decrease of Ag 3 Sn and Cu 6 Sn 5 particles appears to cause a slight increase in Young's modulus, YS and UTS of Zn modified solder. Detailed mechanisms of Ag 3 Sn and Cu 6 Sn 5 suppression and γ-(Cu,Ag) 5 Zn 8 formation were discussed and proposed. |
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