A Numerical Method of Macrosegregation Using a Dendritic Solidification Model, and Its Applications to Directional Solidification via the Use of Magnetic Fields

Abstract

A numerical method for analyzing solidification phenomena of multicomponent alloys is presented. This method consists of macroscopic transport governing equations expressed in terms of a nonlinear multicomponent alloy model, which is coupled with the microscopic dendritic solidification model to estimate permeability. Numerical simulations were performed for channel segregation in a steel ingot and for freckles in a Ni-base IN718 remelted ingot and in Ni-10 wt pct Al directionally solidified (DS) ingots. The results show good agreement with experimental observations. The electromagnetic (EM) braking effect by static magnetic field was incorporated into the numerical method, and the anisotropic behavior of magnetic field was investigated on the DS Ni-10 wt pct Al ingots. Application of relatively low magnetic fields in the transverse to the growth direction (Bx or By) resulted in formation of distorted freckles as a result of the nonuniform liquid flow induced in the transverse direction. It is shown that a considerably high magnetic field is required to suppress the distorted freckles and other freckles developed in longitudinal direction. However, there is a risk of the breakdown of DS. On the other hand, when applying the magnetic fields parallel to the growth direction (Bz), the number of freckles inversely increased at low magnetic fields, but the freckles were eliminated by about the same level of high magnetic field as that of Bx or By. Because the parallel magnetic field suppresses the liquid flow vector components uniformly within the transverse plane, the nonuniform flow does not occur in the transverse directions. As a result, it suppresses the flow in the growth direction. It is envisioned that the application of the parallel magnetic field is beneficial in the commercial production of DS castings.