Effect of zinc-addition and temperature on the work-hardening characteristics of Pb-Sn eutectic alloy

The plastic deformation behaviour of Pb-61.9 Sri and Pb-61.9 Sn-1 Zn alloys have been investigated in isothermal tensile tests, performed within the temperature range 353-413 K at a constant strain rate of 2 x 10(-4) s(-1). The results show that the stress-strain response is sensitive to both temperature and zinc content. The coefficient of work hardening, the yield stress and the fracture stress generally decrease with increasing temperature and Zn addition, while the total strain increase. The variations of microstructure with the deformation temperature were investigated by transmission electron microscopy (TEM). The alloy Pb-61.9 Sn-1 Zn proved to be promising in that it gave high superplastic properties compared with the Pb-61.9 Sri binary eutectic, which was possible mainly due to the existence of Zn. The Zn particles promoting the coarse precipitates and reduce the capabilities for precipitation hardening, while keeping a refined grain size. The hardening effect of precipitates is calculated using the Ashby model, a good agreement is found between the calculated and the experimental values.