Numerical Prediction of Channel-Type Segregation Formation in DC Casting of Al–Mg Billet.

Although channel-type macro-segregations are a well-known defect formed in Direct Chill (DC) casting of aluminum alloys, their formation mechanism remains unclear up to now. To investigate the possible mechanisms, we carried out numerical simulation considering thermo-solutal flow and solidification coupled with phase diagram. The main emphasis is placed on the effect of shrinkage flow and slurry flow on the macro-segregation characteristics. The shrinkage flow causes negative segregations to form along the center axis of billet especially at high casting speeds, while channel-type segregations are not formed under these conditions. On the other hand, the slurry flow in mushy zone results in formation of the channel-type segregations in large billets at low casting speeds. In addition, formation of three types of channel-type segregations is predicted in the following locations (1) flow separation zone, (2) flow stagnant zone, (3) mushy zone where the upward solutal buoyant flow is generated. The formation condition of channel-type segregation is considered using solutal Rayleigh number for binary alloys. [ABSTRACT FROM AUTHOR]