The effect of free-floating dendrites and convection on macrosegregation in direct chill cast aluminum alloys Part I: model development

To obtain a better understanding of the evolution of macrosegregation durin g the direct chill casting of aluminum alloys, a binary mixture model has b een developed that accounts for the redistribution of alloying elements thr ough the transport of free-floating dendrites and fluid flow in the melt an d mushy zones of a solidifying ingot. Separate and distinct mixture momentu m equations are employed to account for momentum transfer in two-phase regi ons which include a slurry of free-floating dendrites and a rigid solid mat rix. A scaling analysis revealed that the flow of liquid and free-floating dendrites is controlled by a balance between buoyancy forces arising from m ixture density variations and the development of an adverse pressure gradie nt. In a companion paper, the model is used to predict macrosegregation in Al-4.5 wt% Cu and Al-6.0 wt% Mg billets. (C) 1999 Elsevier Science Ltd. All rights reserved.