Effect of Cu Particles on the Properties of Sn-Bi-Pb Low-Melting-Point Alloys

The microstructure, phase composition, melting characteristics, and mechanical properties of Sn40Bi40Pb low-melting-point alloys with different amounts of added Cu particles were investigated using scanning electron microscopy (SEM), simultaneous thermogravimetry/differential thermal analysis (TG-DTA), x-ray diffraction (XRD), and electronic universal material testing machines. The results showed that Sn40Bi40Pb was mainly composed of a Sn-(Bi, Pb) solid solution phase, a Bi-(Pb) solid solution phase, and a Pb₇Bi₃ compound phase, with a melting point of 94.017°C, tensile strength of 34.9 MPa and elongation of 64.3%. The (Sn40Bi40Pb)xCu (x = 0.3 wt.%, 0.5 wt.%, 0.7 wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%) alloy consisted of a Sn-(Bi, Pb) solid solution phase, a Bi-(Pb) solid solution phase, a Pb₇Bi₃ intermetallic compound phase, and an η′-Cu₆Sn₅ intermetallic compound. With increasing Cu particle content, the matrix structure gradually refined, dendrite sizes obviously decreased, and the melting range of the alloy first decreased and then increased. However, the temperature change was very small. When the content of Cu particles was 1.5 wt.%, the microstructure and mechanical properties of the alloy were optimal, with tensile strength, elongation, and microhardness of 40.9 MPa, 43.7%, and 17.6 HV, respectively, and a melting point of 94.614°C.