Superplasticity in a relatively low melting point Sn-31.1Pb-3.4Zn solder alloys

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 x 10(4) to 1.0 x 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 sigma)/d(log <(\&epsilon;)over dot>) are strong functions of strain rate and temperature. The log sigma - log <(\&epsilon;)over dot> 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-31.1Pb3.4Zn exhibits optimum superplastic behaviour at 393 K and has a strain rate less than 1.0 x 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. (C) 2003 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim.