The microstructure and properties of as-cast Sn-Zn-Bi solder alloys
2012
Research on the lead-free solders has attracted wide attention, mostly as the
result of the implementation of the Directive on the Restriction of the Use
of Hazardous Substances in Electrical and Electronic Equipment. The Sn-Zn
solder alloys have been considered to be one of the most attractive lead-free
solders due to its ability to easily replace Sn-Pb eutectic alloy without
increasing the soldering temperature. Furthermore, the mechanical properties
are comparable or even superior to those of Sn-Pb solder. However, other
problems still persist. The solution to overcoming these drawbacks is to add
a small amount of alloying elements (Bi, Ag, Cr, Cu, and Sb) to the Sn-Zn
alloys. Microstructure, tensile strength, and hardness of the selected
Sn-Zn-Bi ternary alloys have been investigated in this study. The SEM-EDS was
used for the identification of co-existing phases in the samples. The
specimens’ microstructures are composed of three phases: Sn-rich solid
solution as the matrix, Bi-phase and Zn-rich phase. The Bi precipitates are
formed around the Sn-dendrit grains as well as around the Zn-rich phase. The
amount of Bi segregation increases with the increase of Bi content. The
Sn-Zn-Bi alloys exhibit the high tensile strength and hardness, but the
values of these mechanical properties decrease with the increase of Bi
content, as well as the reduction of Zn content. The results presented in
this paper may offer further knowledge of the effects various parameters have
on the properties of lead-free Sn-Zn-Bi solders.
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