Influence of minor additions of silver on the structural hardening of lead-cadmium-tin alloys

Abstract

The evolution toward equilibrium of the supersaturated Pb-1.5%Cd-0.15%Ag-1.25%Sn alloy has been studied by various techniques, such as hardness, optical microscopy, scanning electron microscopy and electron microprobe. The explored temperatures are 20 and 80°C. The precipitation hardening mechanisms of this alloy are similar to those of silver-free alloys. The as-quenched structure transforms toward equilibrium in a two stage process. In the first stage, called ageing, two transformations take place at the same time: a continuous hardening precipitation and a discontinuous, incomplete, softening transformation. The second stage is characterized by a discontinuous lamellar reprecipitation. The microstructure of this alloy is characterized by the presence of Ag₅Cd₈ precipitates and of zones corresponding to the eutectic mixture. The main effect of silver is to increase hardness by about 2 HV.