Modeling of transport phenomena in continuous casting of non-dendritic billets

Abstract

A macroscopic model for simulating the phase change process and transport of solid fraction is developed for the case of solidification during direct chill continuous casting of a non-dendritic Al-alloy billet, in presence of electromagnetic stirring. MaxwellÕs equations are solved to obtain the electromagnetic force field, which is incorporated in the momentum conservation equations as body force source terms. Thereafter, the complete set of equivalent single-phase governing equations (mass, momentum, energy, species conservation and transport of solid fraction) are solved using a pressure-based finite volume method. A variable viscosity approach is employed to model fluid flow in presence of phase change. The model is first validated against some experimental and numerical results available in the literature, pertaining to the case of conventional continuous casting without any externally imposed stirring. The model predicts the temperature, velocity, species and most importantly, the solid fraction distribution in the mold. These predictions are then used for studying the influence of initial superheat, stirring intensity and cooling rate on the macroscopic behavior of the system.

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part I—Experimental Studies

“…[1] However, movement of the solid phase during equiaxed solidification plays an important role in macrosegregation and microstructure formation that leads to inhomogeneity in casting properties. [2][3][4][5][6][7][8][9] Grain movement is influenced by drag effects caused by melt convection and buoyancy. Buoyancy can cause the grains to sediment or float depending on their density relative to that of the bulk melt.…”

Influence of Transport Mechanisms on Macrosegregation Formation in Direct Chill Cast Industrial Scale Aluminum Alloy Ingots

“…1(a)]: by the melt flow induced by thermosolutal natural convection, shrinkage, and pouring, and by the transport of solute-lean free-floating grains. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] A commonly observed, surface-to-surface distribution of alloying elements at a transverse cross-section of a DC cast ingot is shown in Figure 1(b), revealing distinct regions of positive (solute-rich) and negative (solute-depleted) segregation. [1,3,17,18] A solute-depleted region is present in the ingot center, adjoined by a positive segregation zone spreading into the outward radial direction, an adjacent thin negative segregation zone and another positive segregation layer at the surface.…”

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part II—Numerical Studies

“…[15] It is known also that macrosegregation can become severe if there is movement of solid crystals in the form of motion of equiaxed grains. [3][4][5][6][7][16][17][18][19][20][21][22] The motion of the equiaxed grains affects all aspects of the coupled highly nonlinear transport phenomena viz. heat transfer, solute transport, and flow behavior, all of which make the transport phenomena complex.…”

“…Toward modeling the motion of solid crystals during solidification in a single-phase, onedomain framework, Vreeman et al [16] developed a binary mixture model that accounts for the redistribution of alloying elements through the transport of freely floating dendrites. Recently, Kumar and Dutta [17] presented an approach for predicting the solid fraction distribution during solidification with electromagnetic stirring in the semisolid slurry by solving an additional conservation equation for the transport of fragmented dendrites. However, it may be noted that the models of Vreeman et al [16] and that by Kumar and Dutta [17] considered solid-phase motion as part of columnar solidification where dendrite fragmentation occurs and are, therefore, not applicable to a situation involving equiaxed solidification only.…”