The eutectic alloy Sn-9Zn was considered as a potential alternative to lead-tin solder alloys when compared with other solders. In this paper, ternary, quaternary and penternary additions of the elements Bi, Cu and In were added to the eutectic alloy as a trial to improve its properties. The results showed that, the penternary alloy has properties superior to those of the binary, ternary and quaternary alloys. The alloy of composition Sn-9Zn-1Bi-2Cu-2In has the most suitable properties as a candidate alloy for lead-free solder. It has a lower melting point, 186°C, which is very close to that of Sn-37Pb solder, a lower value of electrical resistivity, 16.5 µΩ.cm, compared with that of Sn-37Pb (17 µΩ.cm), higher value of the Young's modulus, 47 GPa, compared with 45 GPa of Sn-37Pb and a higher value of the Vickers hardness, 191 MPa, compared with 129 MPa of Sn-37Pb eutectic alloy.
In the present paper, the influence of 1, 3, 5 and 10 % Bi (weight %) as ternary additions on structure, melting and mechanical properties of rapidly solidified Sn-3.5Ag alloy has been investigated. The effect of Bi was discussed based on the experimental results. The experimental results showed that the alloys of Sn-3.5Ag, Sn-3.5Ag-1Bi and Sn-3.5Ag-3Bi are composed of two phases; Ag 3 Sn IMC embedded in Sn matrix phase, which indicated that the solubility of Bi phase in Sn-matrix was extended to 3 % as a result of rapid solidification. Bi precipitation in Sn matrix was only observed in Sn-3.5Ag-5Bi and Sn-3.5Ag-10Bi alloys. Also, addition of Bi decreased continuously the melting point of the eutectic Sn-3.5Ag alloy to 202.6 ºC at 10 % Bi. Vickers hardness of Sn-3.5Ag rapidly solidified alloy increased with increasing Bi content up to 3 % due to supersaturated solid solution strengthening hardening mechanism of Bi phase in Sn matrix, while the alloys contain 5 and 10 % Bi exhibited lower values of Vickers hardness. The lower values can be attributed to the precipitation of Bi as a secondary phase which may form strained regions due to the embrittlement of Bi atom. In addition, the effect of Bi addition on the micro-creep behavior of Sn-3.5Ag alloy as well as the creep rate have been described and has been calculated at room temperature.
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