Solidification phenomena related to direct chill casting of aluminium alloys: fundamental studies and future challenges

The principal mechanisms of structure and defect formation during solidification of direct chill (DC) cast billets are reviewed, drawing largely on the results of studies carried out over the past 10 years at Delft University of Technology and the Materials innovation institute. These studies have demonstrated the complexity of mechanisms involved in the formation of structure, macrosegregation and hot tearing and the power of coupled modelling and experimental work in elucidating these phenomena, e. g. relating as cast microstructure to the temperature distribution and flow patterns in the sump of a billet. Control over structure formation and elimination of casting defects can be achieved only when the contributions of all the mechanisms involved and the ratio of these contributions are taken into account. Some immediate challenges for future research are identified.