Microstructure and mechanical properties of the In–48Sn–xAg low-temperature alloy

Alloys with melting points < 150 °C are required for the development of flexible consumer devices. While the eutectic In–48Sn alloy is a promising candidate for these applications, its low tensile strength and low creep resistance during solid-state aging are of concern. The addition of Ag can address this issue to some extent; however, the effect of added Ag on the properties of the alloy is not well understood. Here, we studied the effects of added xAg (x = 0.5, 1.0, 1.5 wt.%) on the fusion start temperature, microstructure, and mechanical properties of the In–Sn eutectic alloy and found that the fusion start temperature of the In–48Sn–xAg alloy was reduced to around 113 °C due to the ternary eutectic reaction of In–Sn–Ag, in which e-AgIn2 only formed in the In–48Sn–xAg alloys. In addition, smaller β-In3Sn and γ-InSn4 phases were produced through the formation of e-AgIn2, which affected the mechanical properties of the alloy. In–48Sn–1.5Ag, with the smallest grains, exhibited the highest tensile strength of 12.5 MPa via boundary strengthening. In–48Sn–1.5Ag fractured in transgranular mode, which is different from the intergranular fracturing of the eutectic alloy with relatively large grains. Conversely, In–48Sn–0.5Ag, with the highest soft-β-In3Sn/hard-γ-InSn4 ratio, showed the longest elongation of 64%, which is twice that of the eutectic In–48Sn alloy.