Study on the evolution mechanism of non-equilibrium solidification microstructure of AlSi10Mg alloy additive manufactured by LPBF

Abstract Throughout the Laser Powder Bed Fusion (L-PBF) procedure, the solidification microstructure constitutes a crucial element in determining the service performance of the formed components. Nevertheless, the solidification of the melt pool exhibits a nonlinear characteristic, the interaction of multiple fields, and high-temperature dynamic evolution. Traditional experimental methods make it difficult to directly observe this process, which significantly complicates the in-depth comprehension of the evolution mechanism of the L-PBF solidification microstructure and restricts process optimization. For this reason, in this paper, with AlSi10Mg alloy as the research object, a powder bed model is established through bidirectional coupling of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD), obtaining the temperature and scale information within the melt pool. A dynamic solidification condition model is constructed and coupled with the Phase Field (PF) model for calculation, disclosing the evolution mechanism of the non-equilibrium solidification microstructure of AlSi10Mg alloy under different process parameters. The research findings indicate that the primary α-Al predominantly takes the form of columnar grains, and the growth process mainly undergoes four stages: planar growth, interface instability, competitive growth, and stable growth. As the laser power reduces, the cooling rate within the melt pool accelerates, leading to the refinement of the primary α-Al grains and an enhanced solute capture effect, which mitigates the microsegregation of solute elements. The simulation results agree with the experimental results. The research outcomes of this paper can serve as guiding and referential significance for the prediction of L-PBF solidification microstructure and process optimization.