Investigation of Macrosegregation Formation in Aluminium DC Casting for Different Alloy Systems

Direct chill (DC) casting of aluminum involves alloys employing different solute elements. In this article, a qualitative analysis and comparison of macrosegregation formation is presented for three different alloy systems: Al-Mg, Al-Zn and Al-Cu. For this purpose, a multiphase, multiscale solidification model based on a volume-averaging method accounting for shrinkage-induced flow, thermal-solutal convection and grain motion is used and applied to an industrial-scale DC-cast ingot. The primary difference between these alloys is the thermal-solutal convection with Al-Mg having a competing thermal and solutal convection, whereas the other two systems have a cooperating thermal and solutal convection. In the study, the combined effect of the macrosegregation mechanisms is analyzed for each alloy to assess the role of the alloy system on the final macrosegregation.

     

A Simplified Three-Phase Model of Equiaxed Solidification for the Prediction of Microstructure and Macrosegregation in Castings

Macrosegregation is a result of the interplay of various transport mechanisms, including natural convection, solidification shrinkage, and grain motion. Experimental observations also indicate the impact of grain morphology, ranging from dendritic to globular, on macrosegregation formation. To avoid the complexity arising due to modeling of an equiaxed dendritic grain, we present the development of a simplified three-phase, multiscale equiaxed dendritic solidification model based on the volume-averaging method, which accounts for the above-mentioned transport phenomena. The validity of the model is assessed by comparing it with the full three-phase model without simplifications. It is then applied to qualitatively analyze the impact of grain morphology on macrosegregation formation in an industrial scale direct chill cast aluminum alloy ingot.