Abstract: To clarify the relationship between externally solidified crystals (ESCs) and other defects, e.g., defect bands and pores, two dimensional (2D) and three dimensional (3D) characterization methods were adopted to analyze castings produced using a modified ingate system equipped with and without an ESC collector. The reduction of ESCs strongly reduced defect band width and shrinkage pore quantity. By reducing the quantity and size of ESCs, net-shrinkage pores were transformed into isolated island-shrinkage pores. We determined via statistical analysis that the mechanical properties of high pressure die castings were strongly related to the size and fraction of the ESCs rather than porosity volume. The reduction of ESCs also caused tensile transgranular fracture modes to transform into intergranular fracture modes. Additionally, casting pressurization strongly reduced pore morphology, volume, and size.