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

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 air‐cooled 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−1, 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.