Microstructure and elevated-temperature shear strength of Zn–4Al–3Mg–xSn high-temperature lead-free solders

•Shear strength of Zn–4Al–3Mg–xSn alloys was tested by shear punch testing at high temperatures.•Yield and ultimate shear strength decreased with increasing test temperature.•Increasing Sn content of alloys decreased shear strength at all temperatures.•Lower strength was due to the soft Sn-rich phase and lack of hard Mg–Zn particles.•The lower volume fraction of the eutectic structure also decreased the shear strength.

The microstructure and shear strength of the high-temperature Zn–4Al–3Mg, Zn–4Al–3Mg–7Sn, and Zn–4Al–3Mg–13Sn solder alloys were investigated in the temperature range of 25–200 °C. The results revealed that the shear yield stress (SYS) and ultimate shear strength (USS) of all three alloys decrease with increasing test temperature. The ternary base alloy showed higher strength levels up to 145 °C, above which all alloys behave similarly. The superiority of the ternary alloy is ascribed to the higher volume fraction of the fine α−η eutectic and eutectoid structures and the hard MgZn2 and Mg2Zn11 particles. Introduction of Sn into the base alloy, however, resulted in substantial decrease in the strength, due to the presence of the soft Sn that reduces the volume fraction of the eutectic structure and the hard second phase particles. Despite the weakening effects of Sn, the strength of quaternary alloys is still higher than those of the Zn–Sn and Pb–Sn high-temperature solders.