Impression creep behavior of Zn-4Al-3Mg-xSn high-temperature lead-free solders

The microstructure and impression creep behavior of the high-temperature Zn-4Al-3Mg-xSn (x = 0, 7, and 13 wt.%) alloys were studied under constant punch stress in the range of 50-800 MPa and at temperatures in the range of 345-473 K. The results showed that for all loads and temperatures, addition of Sn to the base alloy results in higher creep rates, and thus lower creep resistances. The inferior creep behavior of the quaternary alloys is ascribed to the presence of the soft Sn that reduces the volume fraction of the fine α-η eutectic and eutectoid structures, and the hard MgZn2 and Mg2Zn11 second phase particles. Despite the deteriorating effects of Sn, the creep resistance of the quaternary alloys was still higher than those of the Zn-Sn and Pb-Sn high-temperature solders. The stress exponents of 4.0-7.9 and activation energy values of 51.6-92.6 kJ mol− 1, are indicative of a dislocation climb controlled creep mechanism. Dislocation climb controlled by pipe diffusion is the rate controlling mechanism at low temperatures, whereas dislocation climb controlled by lattice diffusion is the dominant creep mechanism at high temperatures.