Macrosegregation in horizontal direct chill casting of aluminium slabs

Abstract

A model for macrosegregation is applied to horizontal direct chill casting (HDC) of Al–4·5 wt-%Cu. The fluid flow in liquid is controlled by thermosolutal buoyancy, as well as shrinkage during solidification and the liquid metal inlet jet. Buoyancy acts perpendicularly to the casting direction and the top and bottom heat transfer rates are not symmetric as in vertical direct chill casting. The influences of casting speed, position of inlet jet and inlet superheat are examined. Significant asymmetry is seen in the flow patterns and macrosegregation profiles. The mixture composition profiles of Cu in the solid show strong subsurface enrichment at the bottom surface and less at the top. Casting speed influences segregation levels and the shape and depth of sump. The placement of the inlet at the top or the bottom of the ingot changed the flow pattern, except near the mushy zone, but did not have an important effect on the exit composition profiles compared to centreline entrance cases.