Abstract
End chill experiments were performed on aluminium and Al–4·5Cu (wt-%) in order to study the effect of melt superheat (20–150 K), chill material (copper, iron, or sand), and specimen length (890–230 mm) on the type and size of macrostructure. Increasing melt superheat increases the length of columnar zone, which is shorter for the alloy than for the commercial purity metal. The columnar fraction increases with the thermal conductivity of the chill material and the heat transfer coefficient. The results are correlated with the temperature gradient, solidification rate, and growth rate obtained from a heat flow model. The columnar to equiaxed transition is found to occur at a critical temperature gradient and growth rate. These critical values differ with alloy composition. The grain size of columnar and equiaxed grains is found to follow a power relationship with solidification rate.
MST/1709
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