Wettability of Sn–Zn, Sn–Ag–Cu and Sn–Bi–Cu Alloys on Copper Substrates

Abstract

The wettability of Sn–9mass%Zn and Sn–3mass%Ag–0.5mass%Cu eutectic alloys and the new lead-free alloys Sn–17mass%Bi–0.5mass%Cu and Sn–30mass%Bi–0.5mass%Cu on a Cu substrate has been investigated by the sessile drop method in Ar atmosphere as a function of time and temperature. The wetting time for Sn–Bi–Cu alloys is much longer than that for Sn–3mass%Ag–0.5mass%Cu eutectic alloy at their liquidus or eutectic temperature. However, the Sn–9mass%Zn alloy has poor wettability on a Cu substrate since Zn may be oxidized to ZnO, resulting in ZnO covering the surface of the droplet. The contact angles of the ternary alloys on a Cu substrate do not decrease monotonically with increasing temperature but do change with time. The wettability on a Cu substrate increases in the order Sn–9mass%Zn, Sn–3mass%Ag–0.5mass%Cu, Sn–17mass%Bi–0.5mass%Cu, Sn–30mass%Bi–0.5mass%Cu, as indicated by their contact angles of 115.8, 49.6, 37.6 and 27.1°, respectively, at 523 K. The addition of Bi clearly greatly improves the wettability of the alloys.