Microstructural Evolution and Mechanical Properties of Sn‐58Bi Solder Alloys with Different Cooling

Abstract

Herein, influences of air-cooling, water-cooling, and liquid nitrogen-cooling (LN-cooling) on microstructures and mechanical properties of Sn-58Bi alloy are studied. It is observed that nearly complete eutectic structures are obtained in aircooled Sn-58Bi alloy. Fine grains and many low-angle grain boundaries (LAGBs) are obtained in water-cooled Sn-58Bi alloy. The LN-cooling method causes Bi atoms to form large, regular rectangular shapes, and there are many high-angle grain boundaries (HAGBs) distributed inside the specimen. Impact tests are performed at room temperature. When the impact rate is 0.98 m s À1 , the fracture energy of the water-cooled Sn-58Bi alloy peaks to 71.5 mJ. The fracture of the LN-cooled impact specimen has a large cleavage step due to the interaction of cleavage cracks and the HAGBs. These experimental results lay the relevant theoretical foundation for the practical application of Sn-58Bi solder alloys.