Effects of aging time on the mechanical properties of Sn-9Zn-1.5Ag-xBi lead-free solder alloys

The effects of aging time on the mechanical properties of the Sn-9Zn-1.5Ag-xBi lead-free solder alloys are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive spectrometry (EDS) and a universal testing machine. The experimental results show that the microstructure of Sn-9Zn- 1.5Ag-xBi solder alloys is composed of Sn-rich phase and AgZn₃. No other intermetallic compounds (IMCs) with Bi content was observed in the solder matrix for Sn-9Zn-1.5Ag solder alloys with various Bi contents before and after aging at 150 °C for different durations. The lattice parameter increases significantly with increasing aging time or Bi addition. The size of Sn-rich grain increased gradually with aging time increased, but decreases with Bi content increases. The maximum yield strength is 112.7 2.2 MPa for Sn-9Zn-1.5Ag-3Bi solder alloy before aging.