Geometrically complex, as-cast, aluminum alloy components offer substantial economic and design advantages as compared with many thermomechanical processing routes. However, the occurrence of potential defects, including porosity, intermetallics, and hot-tears, remains an issue. Using these three defects as examples, recent developments in methodologies for quantifying defect evolution and microstructure using 3D images captured in situ via x-ray microtomography are discussed. It is demonstrated that 3D quantification techniques can provide significant new insight into the mechanisms controlling defect formation, and how microstructure morphology affects component performance.