Macrosegregation Mechanisms in Direct-Chill Casting of Aluminium Alloys

This review paper summarizes the results of recent studies on different mechanisms of macrosegregation upon direct-chill (DC) casting of aluminium alloys. In general, the main mechanisms of macrosegregation have been identified quite some time ago as thermo-solutal convection, free-moving crystals, shrinkage- and deformation-induced flow, and forced convection. Despite this general knowledge, the separation of the effects of these mechanisms on the overall macrosegregation pattern and the ratio of their contribution remained largely unexplored. With the advances in computer simulations and in experimental techniques it becomes possible to look at the impact of individual mechanisms in relation to the macroscopic parameters of the transition region of a DC cast billet and to the microscopic parameters of billet structure. Our systematic research helps in interpreting the apparently contradictory experimental macrosegregation profiles reported in literature. Paper is illustrated by own experimental and computer-simulation results.