Microstructure and mechanical properties of Sn–Bi, Sn–Ag and Sn–Zn lead-free solder alloys

Abstract

The aim of this paper is to develop a comparative evaluation of mechanical properties of as-cast Sn–Bi, Sn–Ag and Sn–Zn alloys as a function of the resulting microstructural arrays with a view to application as solder materials. The resulting microstructures, ultimate and yield tensile strengths and elongations of Sn–40wt.% Bi, Sn–3.5wt.% Ag and Sn–9wt.% Zn alloys were examined and compared with the corresponding results of the traditional Sn–40wt.% Pb solder alloy. Tensile tests were carried out using specimens selected from specific positions along the length of the directionally solidified castings and Hall–Petch type correlations have been proposed relating the resulting tensile properties of each alloy to a parametric scale of the microstructure. It was found that all Pb-free alloys examined comply with a compromise between compatible mechanical strength and environmental protection. The Sn–Bi alloy has the highest ultimate tensile strength of all alloys examined, while both Sn–Ag and Sn–Zn alloys are lighter and exhibited higher ductility than the Sn–Pb and Sn–Bi alloys.