Study of off-eutectic Zn–xMg high temperature solder alloys

Researchers have been working for some times to develop a Pb-free substitute for high-Pb containing solders in electronics. In this study the effect of Mg content on microstructure, melting behavior, thermal, electrical and mechanical properties of a new high-temperature Pb-free solder based on binary Zn–Mg alloy were investigated. The nominal compositions of Zn–xMg (x = 0.5–6.0) alloys were synthesized by conventional melting and casting route. The microstructures of the solders changed significantly on adding Mg content. Higher Mg containing alloys were found rich in intermetallic phases. The formation of the Mg₂Zn₁₁ and metastable MgZn₂ intermetallic phases were identified and were also quantified by X-ray diffraction analysis. The presence of higher amount of intermetallic compounds in hypereutectic Zn–Mg systems deteriorated the tensile properties of the binary alloy. The results of electrical resistivity test indicated that the Mg could elevate the resistivity of newly developed Zn–Mg alloys. The melting behavior of the solder alloys studied by differential thermal analysis (DTA) analysis revealed that the melting temperature range of the solder alloys narrowed with Mg addition. Thermal mechanical analysis (TMA) analysis revealed that the co-efficient of thermal expansion (CTE) decreased on increasing Mg content.