In-situ synchrotron X-ray imaging and quantitative analysis of grain dynamics in semi-solid metal under shear flow

Direct observation of mesoscale grain behaviour during semi-solid metal flow has remained significantly challenging, limiting our understanding of flow-induced defects formation. In this study, in-situ synchrotron X-ray imaging is used to quantitatively analyse grain motion, deformation, fragmentation and grain-to-grain contact interactions in a semi-solid Al-15Cu alloy subjected to controlled shear. The results reveal spatially heterogeneous grain fragmentation across zones with varying shear rates. Grain dynamics demonstrate coordinated movement between solid and liquid phases, with displacement closely correlated with local flow velocity. Force chains aligned with the flow direction facilitates grain rearrangement by promoting grains packing parallel to and separation perpendicular to the flow. The contact network evolves from initial densification to dilatancy-driven loosening, reflecting dynamic rearrangement under shear. These quantitative relationships between flow conditions and grain behaviour offer foundational insights into the precursor mechanisms of defect nucleation, advancing predictive modelling for casting processes.