Assessment of room-temperature short-term stress relaxation and strain relaxation with recovery in Sn-Bi lead-free solders solidified under rotating magnetic field

Abstract

In this paper, short-term stress relaxation test (SRT) as well as strain relaxation and recovery test (SRRT) were performed to assessment the minimum creep rate of Sn-Bi solder from the primary creep stage at 25 °C. Both techniques allow to determination the effect of rotating magnetic field (RMF) during solidification of Sn-Bi solder on the viscous stress exponents nv and other parameters, and have been established to be appropriate for assessment the initial microstructure dependent flow properties of the alloy solder. Additionally, the viscous strain rate in irreversible viscous flow is developed during primary creep and a power-law relationship was created from experimental data to predict the creep deformation mechanism. It was found that the Sn-Bi solder solidified under RMF had the higher resistance to stress and strain relaxation than that solidified without RMF. The stress exponent values of 9.4–6.3 for dislocation creep were achieved depending on the initial imposed strain, and indicating the role of RMF on refining β-Sn dendrites that affect the density of mobile dislocations. Significant decrease in undercooling (from 13.4 to 5.6 °C) was attained after applying RMF, which has good prospects for industrial application.