Multiphysics modeling of mixing and material transport in additive manufacturing with multicomponent powder beds

A key challenge in additive manufacturing (AM) of aluminum-based parts has been the formation of cracks and porosity during the processes. Multicomponent powder beds containing high-melting temperature, highly reactive elements (e.g., Zr and Sc) show promise for improving processibility and reducing crack and pore formation in such alloys. Melting and mixing of these elements in the base alloy during the AM process is yet to be fully understood. This paper describes a multiphysics modeling approach for investigating melt pool dynamics, keyhole and pore formation, and mixing phenomena in multicomponent powder beds. The discrete element method (DEM) is used to generate powder beds with randomly distributed particles of varying sizes. A thermal multi-phase flow model is coupled with a laser welding model in this approach, which includes multiple thermophysical phenomena and laser-material interactions. The multiphysics model was validated using available experimental results in the literature. Through this approach, not only the melt pool dynamics and keyhole morphology, but also the pore formation and mixing evolution during the AM processes, can be quantified for a wide range of process parameters (e.g., laser power and scan speed). To demonstrate the efficacy and application of this method, we thoroughly investigated the additive manufacturing of an Al - Zr powder bed system. The results reveal that the mixing of the alloying element, Zr, is heavily influenced by flow patterns in the melt region and keyhole formation.