Controlling the formation of microstructure at the melt-pool boundaries during directed energy deposition of aluminum alloy with a modified continuous growth restriction factor

Understanding the formation of solidified microstructures adjacent to the fusion boundary of a melt pool can provide valuable insights for optimizing process parameters and achieving the desired microstructure in directed energy deposition (DED). However, existing analytical models fail to consider internal and external factors, particularly the solute concentration and scan speed, leading to low prediction accuracy of the solidified microstructure. A v c model of grain growth rate is developed based on the continuous growth restriction factor Q C , that considers the coupling effect of both the internal factors and external factors. Q C can also be used to describe the evolution of the growth restriction factor Q along the solidification path of liquid metal within the melt pool. The v c model can accurately predict variations in the rate of grain growth and evaluate the influence of solute concentration and scan speed on the Planar to Cellular Transition (PCT) of the Solid/Liquid interface and grain size. The Q C value increases with the rise of solute concentration and scan speed, resulting in further growth resistance decreasing the v c value, thereby permitting secondary embryos to nucleate only after the S/L interface moves a short distance. This study fills the gap left by the inability of Q to explain the influence of solutes on the microstructure during DED, and presents a novel approach for analyzing the formation mechanism of solidified microstructure adjacent to the fusion boundary of the melt pool.