Structural hardening of lead-cadmium (tin-silver) alloys for battery's grids. I. Lead-cadmium alloys.

The reequilibration of supersatured Pb-Cd alloys was studied by different e xperimental methods: hardness measurements, optical and electron microscopy , electron microprobe. Two structural states were considered: as-cast alloy s, rehomogenised alloys. The Cd contents were 1, 1.5, 2 and 3.2 weight%. Th e explored temperatures were 20 and 80 degrees C. This last temperature cor responds to the curing temperature of battery's grids and to the highest op erating temperature. The evolution of the quenched structure towards the eq uilibrium state was studied for the time range one minute to one year. The corresponding aging is characterized by a continuous precipitation and a di scontinuous transformation. The hardening process is followed by an overagi ng which consists of a discontinuous transformation with a reprecipitation of the Cd from the fine hardening precipitates of the same phase.