Superplasticity in a relatively low melting point Sn–31.1Pb–3.4Zn solder alloy

Abstract

The superplastic properties of Sn–31.1Pb–3.4Zn solder alloy were investigated with respect to the effect of testing temperatures ranging from 353 to 413 K and strain rates ranging from 6 × 10−4 to 1.0 × 10−2 s−1. The results for the true stress–strain characteristics show that the flow stress and strain rate sensitivity parameter m = d(log σ)/d are strong functions of strain rate and temperature. The log σ – log curve shows a sigmoidal shape with an intermediate region of high strain rate sensitivities (maximum 0.55). The activation energy was determined as 36–62 kJ mol−1 and the microstructural analysis was performed after superplastic deformation. The solder alloy proved to be promising in that it gave a good combination of high ductility and low melting temperature by grain refinement. Furthermore, fine-grained Sn–31.1Pb–3.4Zn exhibits optimum superplastic behaviour at 393 K and has a strain rate less than 1.0 × 10−2 s−1. The results show the importance of the grain refinement process in giving Sn–31.1Pb–3.4Zn solder with promising mechanical properties. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)