Effects of Zn addition on microstructure and tensile properties of Sn-1Ag-0.5Cu alloy

Effects of Zn addition on microstructure and tensile properties of Sn-1Ag-0.5Cu alloy were investigated. It was found that after the Zn addition, the Cu6Sn5 and Ag3Sn phases were gradually replaced by the Cu5Zn8, Ag5Zn8 and AgZn3 phases and the amount of them were increased with increasing Zn content. The tensile tests showed that while the elongation of the alloy decreased with increasing Zn content, the strength was increased by Zn additions for Zn content <1 wt.%, but decreased at Zn content of 2 wt.%. The fracture surface analysis and deformed surface observation demonstrated that the fracture of the Sn-1Ag-0.5Cu-2Zn alloy was originated at the Ag5Zn8 phase. TEM observation further confirmed that the Ag5Zn8 phase was the weakness of the microstructure, accounting for the combination of the worst strength and elongation of the Sn-1Ag-0.5Cu-2Zn alloy.