粉末圧延法で作製した鉛蓄電池用Pb基合金格子材料のクリープ挙動

Abstract

For extending the life of a lead-acid battery, the control of the creep of a Pb-base alloy as the grid material is of great importance. In this study, Pb-1.50 mass%Sn alloys were produced by two different processes, namely the cast-rolling process and the powder-rolling one, in order to study the influence of the crystallographic structure on the creep behavior of the Pb-base alloy. The structure produced by the cast-rolling, which is the commonly used process in the lead-acid battery industry, consists of relatively large grains. On the other hand, the powder-rolling is a new process for the preparation of the grid material, which uses air-atomized powders as the raw materials. The mean size of crystal grains of the powder-rolled Pb-base alloy is extremely small in comparison with that of the cast-rolled one. The tensile strength and the Vickers hardness of a Pb-1.50 mass%Sn powder-rolled alloy are 23 MPa and ca. Hv 9.0, respectively. Although these values are twice larger than those of a Pb-1.50 mass%Sn cast-rolled alloy, they are lower than the values of the Pb-base alloy in common use of the VRLA battery, or a Pb-0.08 mass%Ca-1.20 mass%Sn cast-rolled alloy. However, the corrosion creep test showed that the steady creep rate of a Pb-1.50 mass%Sn powder-rolled alloy was extremely smaller than those of all the Pb-base cast-rolled alloys. This finding suggests that the powder rolling process is very effective to improve the creep resistance of a Pb-base alloy as a grid material in a lead-acid battery. It can be also presumed that fine grain size in the powder-rolled alloy of Pb-1.50 mass%Sn function as an obstacle to the movement of dislocation, resulting in remarkably the suppression of the creep rate.