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.