Tensile deformation mechanism of Sn-37Pb solder alloy at cryogenic temperatures

Traditional solder alloy Sn-37Pb is still widely used in some special industries, such as aerospace and military fields, although the use of Pb containing solder is prohibited in the civil market. However, some of the applications, such as external wires of earth satellites and military application equipment of North and South poles, will make the electronic devices face the cryogenic temperatures (up to −150 °C) service conditions, and thus the reliability of solder alloys is seriously threatened. In the field of cryogenic temperature, attentions are always paid to the ductile brittle transition of metal materials, which is also the focus of this study. Thus, we measured the tensile properties of Sn-37Pb at temperatures of −150~0 °C and a tensile rate of 6.67 ×10
⁻⁴
s
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. The yield strength and ultimate strength of Sn-37Pb alloy increased gradually with decreasing the testing temperature. However, the elongation of the alloy was above 8.9% in the temperature range of −100~0 °C, while decreased to 4.8% at −150 °C. Sn-37 Pb alloy rapidly suffered brittle fracture after crossing the ultimate point at −150 °C. In the temperature range of −100~0 °C, there were a lot of dimples in the tensile fracture, which is in good agreement with the ductile fracture of the alloy. At −150 °C, there were a lot of platelike phases in the fracture besides some dimples, this implies that the formation of plate-like phases was the cause of the ultimate brittle fracture. This work provides guidance for the reliability of solder alloy at cryogenic temperatures