Macrosegregation Induced by Floating Grains in Direct-Chill Casting of Aluminum Alloys

The macrosegregation mechanism induced by floating grains in direct-chill casting of aluminum alloys was elucidated. Floating grains consist of interior solute-depleted coarse- and peripheral fine dendrites. During direct-chill casting, some grains freely travel in slurry zone, where the low-temperature gradient results in the slow but unconstrained dendrites growth. The resulting coarse and solute-lean dendrites are then transported to casting center and entrapped by mushy zone, where the periphery fine dendrites subsequently grow.