Effect of isothermal ageing on the electrical resistivity and microstructure of Pb–Sn–Zn ternary alloys

Electrical resistivity measurements (Δρ/ρ0) were carried out on (Pb–65.5Sn–3.4Zn) eutectic and (Pb–65Sn–1.0Zn) ternary alloys, at various ageing temperatures for various ageing times. Both alloys showed enhancement in the reaction rate in comparison to those of binary eutectic Pb–Sn alloy, the variations of microstructure with ageing temperature were investigated by transmission electron microscope (TEM), X-ray, microhardness, and differential thermal analysis (DTA). It was concluded that the Pb–Sn–Zn ternary alloys show progressive reduction in the electrical resistivity compared with the Pb–Sn binary eutectic composition as a result of the nature of the internal stresses induced by the Zn particles and the multiplicity of types of interphase boundary causing enhancement in the driving force for the coarsening process.