Abstract
As the segregation results from both the distribution of solute at the freezing front and the diffusion of it in solid during solidification, the pattern of the segregation should be determined by the processes of crystal growth. Especially in dendrite growth, it is natural that the coalescence and coarsening of dendrite arms should influence the microsegregation. In this paper, the mechanism of solute redistribution in dendrite growth was studied. Al-Cu alloys containing 5.5, 15 and 27% copper were quenched during solidification, and the distribution of copper in dendrites were quantitatively analyzed with Electron Probe Microanalyzer.
The effective distribution coefficient of copper to primary α-phase became larger with increase in cooling rate. This suggests that the larger cooling rate results in the higher solute concentration in the liquid near the dendrite tip.
Copper concentration in the core of dendrite increased with the fraction of solid, and that was greater at lower cooling rate.
The fair difference of concentration between the measured values and calculated ones from Flemings method(13) suggests that the dendrite grows mainly accompanying the coalescence.
