Electrical conductivity in directionally solidified lead-9 and -20 wt pct copper alloys

Abstract

Composites consisting of aligned copper dendrites in a lead matrix have been produced by directional solidification processing for potential application as grids in lead-acid batteries. To promote a uniform composite of aligned copper dendrites in a protective lead matrix, two alloy compositions, Pb-9 and -20 wt pct Cu, have been directionally solidified through a temperature gradient,G l of 4.5 Kmm-1 at constant growth velocities which ranged from 1 to 100 µm s-1. With slow growth rates (≲10 µm s-1 ), the copper dendrites were generally columnar and continuous along the sample length; at higher velocities (≳60 µm s-1), they assumed an intricate and equiaxed morphology. In accordance with copper content and growth rate, the electrical conductivity of the directionally solidified composites was found to be as much as a 2.5 times that of pure lead. The results are compared with that predicted by a model based on a geometrical dendrite.