| To ensure a uniform composite of aligned copper dendrites in a protective lead matrix for possible application as grids in lead-acid batteries, Pb-20wt%Cu alloy has been directionally solidified in a constant temperature gradient, G₁=4.5K/㎜, with constant growth velocities, 10 and 20㎛/sec. The solidification parameters of growth orientation with respect to gravity vector and sample diameter have been correlated with the resulting microstructure. At this slow growth velocity, the rejection of lead-rich liquid by the copper dendrites increases the density of the liquid, leading to convection and consequently, to severe macrosegregation and a non-uniforem structure. A novel technique in which the sample tube is rotated while being solidified in a horizontal position, has been tried and found to promote a uniorem and continuous Cu dendrite morphology. |
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