Melt Conditioned Direct Chill (MC-DC) Casting of Al Alloys

A fine and uniform microstructure is always desirable for aluminium billets produced by direct-chill (DC) casting. Although this is usually achieved by grain refiner addition during DC casting, in this paper we demonstrate a physical approach for grain refining DC cast billets. Intensive melt shearing is applied to DC casting by submerging a rotor-stator based high shear device in the sump of a conventional DC caster. It has been shown that DC casting with intensive melt shearing can achieve one order of magnitude grain size reduction without using chemical grain refiners. Such fine and equiaxed grain structure in the Al billets can be attributed to enhanced heterogeneous nucleation and growth under conditions with reduced temperature gradient and increased growth velocity.