Influences of Ag and In Alloying on Microstructure and Mechanical Properties of Sn-58Bi Solder

Abstract

Ag (2.0 wt.%) and In (1.5 wt.%) were alloyed into Sn-58Bi eutectic solder, and the individual and combined influences of Ag and In on the microstructure, microhardness, and impact toughness of the SnBi solder were investigated. The results reveal that the microstructures of the SnBiAg, SnBiIn, and SnBiAgIn alloyed solders are coarser than that of the SnBi eutectic solder. Fine Ag3Sn particles are formed in the SnBiAg and SnBiAgIn solders, while small regions of In-rich phases appear in the SnBiIn and SnBiAgIn solders. The microhardness of the three alloyed solders are higher than the SnBi solder, and the Sn-rich phases in the alloyed solders show higher nanohardness, while the nanohardness of the Bi-rich phases with Ag and In addition changes little. The impact toughness of the SnBiAg, SnBiIn, and SnBiAgIn solders are observed to be higher than the SnBi solder, especially in the case of the SnBiAgIn solder. The improvement in ductility of the Sn-rich phase induced by the In solution, and the strengthening effect from the Ag3Sn particles are predicated to be the reason for the increase in impact toughness. The fracture surfaces demonstrate that plastic deformation of the SnBiAgIn solder during the impact process is more obvious. Overall, the combined addition of Ag and In can increase the microhardness and impact toughness of SnBi eutectic solder.