Effects of aluminum addition (x = 0–1 wt%) on the thermal behavior, microstructure and mechanical properties of Zn–30Sn high temperature lead-free solder alloy

Abstract

The thermal behavior, microstructure and mechanical properties of the modified lead-free Zn–30Sn–xAl (x = 0, 0.1, 0.5, 1.0 wt%) composite solder alloys had been investigated in the present study. Addition of Al tended to refine the microstructure and decrease the melting point. The analysis of microstructure showed that the supersaturated precipitation of Al (0.5 wt%) in η-Zn phase would result in the formation of Zn–Al phase. Due to the peritectic reaction, the Zn–Sn–Al phase was observed when the Al content was 1 wt%. The refinement of eutectic structure and η-Zn phase improved the elongation when the minor Al element (0.1 and 0.5 wt%) was added into Zn–30Sn solder. However, when the Al content was 1.0 wt%, the elongation of Zn–30Sn-based solder decreased because of the stress concentration. Besides, the ultimate tensile strength (UTS) of the alloy increased from 45.48 to 91.26 MPa, and the yield strength increased from 35.26 to 37.53 MPa. The analysis of the fractography showed that the brittle fracture gradually turned into mixed fracture mode of ductile fracture and ductile fracture with the increasing content of Al.