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

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 temary 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 degrees, respectively, at 523 K. The addition of Bi clearly greatly improves the wettability of the alloys. [doi:10.2320/matertrans.M2011349]