Effect of liquid metal distribution on the flow field and macrosegregation during direct chill casting of aluminum alloy 7050

Abstract

A fully transient 2-D axisymmetric numerical model is used to investigate the effects of liquid metal distribution on the flow field and macrosegregation during DC casting. The model is applied to 500 mm diameter billets of aluminum alloy 7050 cast at 30, 60, and 90 mm/min. The predicted flow fields and composition profiles are compared for three metal feeding systems; one containing only a submerged nozzle, another with the addition of a rigid combo bag, and a final with the addition of a flow diffuser plate. The results from the numerical model show that the flow field and macrosegregation are strongly influenced by the nozzle exit velocity, which is primarily a function of the nozzle to ingot area ratio. For area ratios below 5%, jetting of the nozzle flow down the centerline is predicted, resulting in higher levels of macrosegregation. For area ratios above 5%, jetting of the nozzle flow is not predicted, but oscillations in the flow field at higher casting speeds are. The addition of either a low permeability combo bag or a flow diffuser plate is shown to prevent jetting of the nozzle flow down the centerline and to stabilize the flow field.