Dynamics of material redistribution and microstructure formation in Al-Cu multimaterial

Additive manufacturing (AM) enables the precise fabrication of multimaterial components; however, Achieving chemical and structural homogeneity at material interfaces remains a significant challenge. Existing research on material transport in AM primarily relies on numerical simulations and postmortem analyses, with real-time, three-dimensional characterization still lacking. In this study, we employ in situ X-ray radiography and X-ray computed tomography to investigate material redistribution during laser powder bed fusion of a al-cuCrZr multimaterial. Our results demonstrate that the incorporation of cu occurs through discrete, stochastic events within the melt pool. We suggest that this mode of incorporation results from the poor wetting of the spreading liquid on the substrate liquid, necessitating additional dynamic driving forces to assist the incorporation process. Within the melt pool, copper mixing is predominantly governed by fluid dynamics, with relatively negligible effects from gravitational/buoyancy and viscous forces, as well as diffusion. However, despite the high fluid velocity, heterogeneous local compositions persist. These variation of local composition, in turn, lead to shifts in the local solidification path and ultimately influence the resulting microstructure. The predominant mixing mechanisms and length scales are likely applicable to a wider range of multimaterial systems. Additionally, the incorporation mode could be expected to hold for multimaterial systems sharing similar wetting behavior, but requires further investigations for confirmation. These findings offer valuable experimental validation for numerical models and provide key insights to guide the optimization of future multimaterial AM processes.