Numerical Study of a Direct Chill Slab Caster Fitted With a Porous Filter for Aluminum Alloy AA-2024

Abstract

The present study is undertaken to model an industrial-sized vertical Direct Chill (DC) slab caster fitted with a porous filter near the melt entry region. The modeled alloy is a high strength aluminum alloy AA-2024 which is extensively used by the aerospace industry. The model has incorporated the 3-D turbulent aspect of the melt flow and heat transfer in the liquid sump and the mushy region solidification aspect of this long solidification range (136° C) alloy. The verified 3-D turbulent CFD in-house code is used to study the effects of various parameters of this casting process in order to gain some fundamental understanding of the melt flow and solidification behavior of the process. The studied caster consists of a popular ‘hot-top’ mold fitted with a porous filter above which molten aluminum alloy is delivered with a constant flow-rate across the entire hot-top. Because of two-fold symmetry, a quarter of the domain of the caster is modeled to save computational costs and time. A staggered control volume based finite-difference scheme is used to solve the non-dimensional modeled equations and the associated boundary conditions. The turbulent aspect of the flow in the porous filter is modeled using the latest suggested version of the Brinkman-Forcheimer extended form of Darcy equation for a porous media. The turbulent melt flow and solidification heat transfer in the clear fluid region are modeled using a low Reynolds number version of the k–ε eddy viscosity model. Computed results for the steady-state phase of the casting process are presented for four casting speeds, varying from 100 to 220 mm/min, for three metal-mold contact regions, varying from 20 to 50 mm and for three metal-mold convective heat transfer boundary conditions, varying from 1.0 to 4.0 kW/m2K and all for a fixed inlet melt superheat of 64° C. The permeability of the filter is also varied to ascertain its influence on the predicted results. Computed results of the velocity and temperature profiles, the sump depth and mushy region at the centre of the caster as well as the solidification shell thickness at the exit of the mold are provided and discussed. The present work can provide some useful guidelines in designing and optimizing a vertical DC slab caster for producing good quality casts for the common aluminum alloy AA-2024.