Deformation behavior and constitutive equation of Sn-37Pb solder alloy at cryogenic temperature

In this work, the tensile property, ductile-to-brittle transition (DBT) mechanism and constitutive relations of 63Sn-37Pb (Sn-37Pb) solder alloy at cryogenic temperature were studied by uniaxial tensile experiments for different temperatures. The tensile strength of Sn-37Pb solder alloy increases from 38.2 MPa (293 K) to 178.9 MPa (123 K) and then declines to 145.2 MPa (77 K) with decreases of temperature, and its fracture elongation changes from 42.8% (293 K) to 10.2% (77 K). Mechanical behavior of Pb second phase in Sn-37Pb alloy at low temperatures is illustrated: when the temperature drops to 123 K and below, the fracture failure of beta-Sn matrix occurs in an open mode. As a result, Sn-37Pb solder alloy fails by brittle fracture mode. Anand model is adopted as a unified viscoplastic intrinsic law to describe the intrinsic relationship of Sn-37Pb solder alloys. Above 123 K, Anand model can effectively fit the stress-strain curves of Sn-37Pb solder alloys. When the temperature lower than 123 K, the deformation characters of Sn-37Pb solder alloys change from elastoviscoplastic to elasto-plastic, and Anand model is unable to continue to fit the intrinsic relationship of Sn37Pb solder alloys. Sn-37Pb solder alloy exhibits more obvious strain hardening at low temperature, and its low-temperature intrinsic response is successfully described by Hollomon's equation. The research method of the solder alloy is of great significance to solve the reliability problem of low temperature electronic devices.