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<p>Misrun defects remain a severe challenge in the thin-walled as-cast components. In the present research, a momentum dominated filling algorithm and a laminar flow model are employed to study the solidification process of ternary Al-7Si-0.5Mg thin-walled castings. A critical solid fraction of 0.25 is deduced using iterative computations. The influences of wall thickness on the misrun defects are numerically studied. As shown in the simulation results, castings with 6 and 5&#xa0;mm thicknesses do not have misrun defects, but those with 4 and 3 mm thicknesses have misrun defects. The predicted cooling rate in the leading tip of the filling metal is 2.0, 2.8, 4.4, and 10.1&#xa0;°C/s, as the wall thickness decreases from 6 to 5, 4, and 3&#xa0;mm, respectively. The fluid flow velocity decreases from the maximum to zero within about 0.7 and 1&#xa0;s in the leading tip for castings with 3 and 4&#xa0;mm wall thicknesses, indicating a quick stopping of flowing. Experimental measurements in the 3&#xa0;mm-thin-walled casting show that the average sizes of the equiaxed grains progressively decrease from 675 to 57&#xa0;µm along the melt flow direction. Based on simulations and experimental characterizations, the flow-choking mechanism is identified as the front blocking due to the instantaneous nucleation of numerous equiaxed grains in the leading tip of the filling metal. The formation of a refined equiaxed grain structure at a high cooling rate in a short period of time results in misrun defects. The cooling rate at the leading tip is suggested to be lower than 3.7&#xa0;°C/s to ensure sufficient filling. Consequently, a critical cooling rate of about 3.7&#xa0;°C/s at the leading tip is proposed.</p>

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Numerical Simulation and Analysis of Flow-Choking Mechanism for Misrun Defects of Thin-Walled Al-7Si-0.5Mg Alloy in Gravity Sand Casting

  • 期刊论文

  • 发表日期：

    2025年2月11日

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  • Zhijie Guo,
  • Dong-Rong Liu,
  • Yicheng Feng,
  • Erjun Guo

摘要

Misrun defects remain a severe challenge in the thin-walled as-cast components. In the present research, a momentum dominated filling algorithm and a laminar flow model are employed to study the solidification process of ternary Al-7Si-0.5Mg thin-walled castings. A critical solid fraction of 0.25 is deduced using iterative computations. The influences of wall thickness on the misrun defects are numerically studied. As shown in the simulation results, castings with 6 and 5 mm thicknesses do not have misrun defects, but those with 4 and 3 mm thicknesses have misrun defects. The predicted cooling rate in the leading tip of the filling metal is 2.0, 2.8, 4.4, and 10.1 °C/s, as the wall thickness decreases from 6 to 5, 4, and 3 mm, respectively. The fluid flow velocity decreases from the maximum to zero within about 0.7 and 1 s in the leading tip for castings with 3 and 4 mm wall thicknesses, indicating a quick stopping of flowing. Experimental measurements in the 3 mm-thin-walled casting show that the average sizes of the equiaxed grains progressively decrease from 675 to 57 µm along the melt flow direction. Based on simulations and experimental characterizations, the flow-choking mechanism is identified as the front blocking due to the instantaneous nucleation of numerous equiaxed grains in the leading tip of the filling metal. The formation of a refined equiaxed grain structure at a high cooling rate in a short period of time results in misrun defects. The cooling rate at the leading tip is suggested to be lower than 3.7 °C/s to ensure sufficient filling. Consequently, a critical cooling rate of about 3.7 °C/s at the leading tip is proposed.