Kinetic Study of the Aging and Overaging of Alloy Pb0.058%Ca0.12%Sr1.09%Sn for Battery Grids

Abstract

In this paper, we examine the effect of a small amount of Sn, Sr and Ca on the hardening and the kinetic properties of Pb. Experimentally, we analyze the specific process from the structural hardening evolution to equilibrium of PbCaSrSn alloy occurring in two steps. In the first one, a discontinuous transformation hardening and a continuous precipitation take place. A lamellar discontinuous precipitation that occurs after aging, characterizes the second step. Theoretically, we study the aging and overaging kinetics of the alloy by using the two complimentary methods needed to calculate the apparent activation energies of the Pb0.058%Ca0.12%Sr1.09%Sn associated with the various transformations, characterizing its hardening at 20 and 80 °C. We show that activation energies of aging and overaging of Pb0.058%Ca0.12%Sr1.09%Sn alloy are 25 and 28 kJ/mole, respectively, which are four times lower than the self-diffusion energy of Pb. Moreover, the addition of Ca, Sr and Sn leads to an amplification of the maximum hardness from 5 ± 5% HV to 21 ± 5% HV and an acceleration of the transformation hardening process responsible for aging.