Microstructure and mechanical properties of Sn-Bi lead-free solder during extruding and drawing process

As an important lead-free replacement, Sn-Bi solder alloy has drawn much interest from industry due to its low melting temperature. However, there is a serious concern over its bad plasticity and poor deformation properties. In this paper, the microstructure and mechanical properties of Sn-58Bi solder alloys during extruding and drawing process were investigated using an optical microscopy (OM), an scanning electron microscope (SEM), a CMT4503 electronic universal testing machine and a FM-700 micro hardness tester. The results show that the as-cast eutectic Sn-Bi alloy consisted of network-shaped Sn phase and thick Bi phase. The extrusion force has few effects on the microstructure. But with increasing the extrusion force, the tensile strength and the elongation increased first and then decreased. After drawing, the microstructure of Sn-58Bi solder appeared to be thin fibrous along the direction of drawing. The tensile strength and hardness both increased first and then decreased, while the elongation decreased during the whole drawing process. The effects of temperature on mechanical properties of as-extruded Sn-58Bi solder were also investigated and the results show that the tensile strength decreased with increasing the temperature and the elongation significantly increased to 490% at 100°C.