抄録
Macrosegregation in holizontally solidified Al-5.5%Cu and 14%Mg alloys resulted mainly from fluid flow in the mushy zone which is composed of a number of dendrite arms and some string ghosts. The main driving force for the flow is gravity acting on liquid during solidification.
In this paper, the mushy zone is simulated as porous medium with pipes. Applying D’Arcy’s and Poiseuille’s Laws to the fluid flow in the mushy zone, the flow velocities and the resulting macrosegregation are numerically analyzed. The diameter and distribution of the pipes are decided on the basis of the experimental results on the formation of string ghosts.
The analysis shows that solute-rich interdendritic liquid flows into the bulk liquid through the string ghosts, resulting in a distinctive macrosegregation in the slowly solidified specimens. The calculated effective segregation coefficient (Ke), which is a measure of macrosegregation, decreases with an increase in 1⁄R, thus showing good agreement with the experimental result.
