On The Formation of Extruded Surface Segregation Layer in Aluminum Direct Chill Casting Process

Abstract

The aim of this research work was to develop a mathematical model to study the formation of extruded surface segregation phenomenon during the early stages of solidification in an aluminum direct chill casting process. The mathematical analyses contain a one dimensional mathematical model of heat flow, solidification, interdendritic strain and macrosegregation. Some typical cases in conventional direct chill casting processes related to increase surface segregation and fluctuation in macrosegregation with distance from the ingot surface were simulated. Good agreement was found by previous measurements and simulated results. Model results were discussed to explain the effects of different thermal solidification factors and interdendritic strain on the extruded surface segregation layer phenomenon. The results show that this phenomenon is sensitive to alloy composition and forms in the gap between the ingot surface and mould wall. Also, the model results point out that this phenomenon appears as a direct effect of the extrusion mechanism of interdendritic solute liquid associated with the interdendritic strain distribution in the coherent region in the mushy zone.