Development of a Fluid-Particle Model in Simulating the Motion of External Solidified Crystals and the Evolution of Defect Bands in High-Pressure Die Casting

A numerical fluid-particle model was developed to simulate the motion of external solidified crystals (ESCs) in the melt during the filling process of high-pressure die casting (HPDC). Simulation results on a tensile bar casting with two types of ingates (semi-circle and circle) revealed that for a long time scale the ESCs tended to distribute in a ring pattern around the specimen center, whereas for a short time scale the ESC distribution changed constantly from the ring pattern to either the center pattern or the ring-center pattern. It was proposed that the defect bands would form at these areas where two solidification fronts met (where solidification shrinkage occurred), including one originating from the skin layer of the specimen and the other from the ESC region. Accordingly, three types of defect band patterns, which were commonly observed in HPDC experiment, could be successfully simulated and explained using this model.