Improvement of microstructure and tensile properties of Sn–Bi–Ag alloy by heterogeneous nucleation of β-Sn on Ag3Sn

Abstract

Different weight fractions (0, 0.5, 1.0, 2.0, and 3.0 wt%) of sliver (Ag) were used to dope Sn–Bi eutectic alloys in this study. The microstructure and tensile and thermal properties of Sn–Bi eutectic alloys doped with Ag were investigated. The results indicate that the addition of Ag increases the solidification temperature and reduces the fusing latent heat of alloy, but it has no significant effect on the melting point of the alloy. According to the electron backscattered diffraction (EBSD) analysis and calculation of the disregistry between ε-Ag3Sn and β-Sn, ε-Ag3Sn can be used as the heterogeneous nucleation substrate of β-Sn, thus refining lamellar eutectic spacing. The orientation relationship between the ε-Ag3Sn phase and the β-Sn phase was as follows: [ 0 2‾1 ]Ag3Sn//[ 0 1 2 ]β-Sn, (0 1 2)Ag3Sn//(‾1 2‾1) β-Sn, and [‾1 2 0 ]Ag3Sn//[ 0 1 2 ]β-Sn, (2 1‾1)Ag3Sn//(‾1 2‾1)β-Sn. The tensile strength of the eutectic Sn–Bi alloy with addition of 1.0 wt% Ag reached 72 MPa, which was 20% higher than that of the original alloy. The analysis showed that Ag doping increase the tensile strength of the eutectic Sn–Bi alloy, because of fine grain strengthening and second phase strengthening mechanism