Tensile Properties of Sn-37wt%Bi and Sn-57wt%Bi at Temperatures Below 0°C

Tin (Sn)-Bismuth (Bi) alloys have been studied as low-temperature alternatives of Copper (Cu) containing Lead (Pb)-free solders. Here ‘low-temperature’ relates to the processing temperature as the minimum melting point of Sn- Bi alloys is around 139°C. Meanwhile, service temperatures below O°C can be reached during the use or deployment of electronic devices. The mechanical properties of Sn-Bi alloys in this low-temperature regime are rarely covered in the literature. This work undertook a series of tensile tests with Sn-37wt%Bi (Sn37Bi) and Sn-57wt%Bi (Sn57Bi) alloys to investigate a) the strain rate dependence at O°C and -20°C and b) the temperature dependence of tensile strength and elongation from O°C, -20°C to -40°C, comparing the results to those obtained in previous work at room temperature (RT). It has been found that the ultimate tensile strength (UTS) of Sn37Bi at all temperature levels is higher than that of Sn57Bi, with similar maximum elongation achieved.