• Title/Summary/Keyword: 조대편석

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Solidification Process of an Al-Cu Alloy in a Vertical Annular Mold and Effects of Cooling Rate on Macrosegregation (수직환상주형내 Al-Cu합금의 응고과정 및 냉각속도의 조대편석에 대한 영향)

  • 유호선
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.7
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    • pp.1818-1832
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    • 1994
  • Transport process during solidification of an AI-CU alloy in a vertical annular mold of which inner wall is cooled is numerically simulated. A model which can take account of local density dependence on the solute concentration is established and incorperated in the analysis. Results show that thermally and solutally induced convections are developed in sequence, so that there is little interaction between them. Thermal convection effectively removes the initial superheat from the melt and vanishes as solidification proceeds from the cooling wall. On the other hand, solutal convection which is developed later over the meshy and the pure liquid regions leads to large-scale redistribution of the consituents. The degree of the initial superheating hardly affects overall solidification behavior except the early stage of the process, when the cooling rate is kept constant. Macrosegregation is reduced remarkably with increasing cooling rate, because not only the liquidus interface advances so quickly that time available for the solute transport is not enough, but also the interdendritic flow is strongly damped by rapid crystal growth within the mushy region.

Solidification Process of a Binary Mixture with Anisotropy of the Mushy Region (머시영역의 비등방성을 고려한 2성분혼합물의 응고과정)

  • 유호선
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.1
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    • pp.162-171
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    • 1993
  • This paper deals with the anisotropy of the mushy region during solidification process of a binary mixture. A theoretical model which specifies a permeability tensor in terms of pricipal values is proposed. Also, the governing equations are modified into convenient forms for the numerical analysis with the existing algorithm. Some test computations are performed for soeidification of aqueous ammonium chloride solution contained in a square cavity. Results show that not only the present model is capable of resolving fundamental characteristics of the tranport phenomena, but also the anisotropy significantly affects the interdendritic flow structure, i.e., double-diffusive convection and macrosegregation patterns.

The effect of mold rotation on solidification process of an Al-Cu alloy (주형의 회전이 Al-Cu 합금의 응고과정에 미치는 영향)

  • Yu, Ho-Seon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.4
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    • pp.525-540
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    • 1997
  • The effect of mold rotation on the transport process and resultant macrosegregation pattern during solidification of an Al-Cu alloy contained in a vertical axisymmetric annular mold cooled from the inner wall is numerically investigated. The mold initially at rest starts to rotate at a prescribed angular velocity simultaneously with the beginning of cooling. Computed results for a representative case show that the mold rotation essentially suppresses the development of both thermal and solutal convections in the melt, creating distinct characteristics such as the liquidus front, flow pattern and temperature distribution from those for the stationary mold. Thermal convection which develops at the early stages of cooling is soon extinguished by the rotating flow induced during spin-up, and thus does not effectively remove the initial superheat from the melt. On the other hand, solutal convection, though it weakens considerably and is confined within the mushy zone, still predominates over the solute redistribution process. With increasing the angular velocity, the solute transport in the axial direction is enhanced, whereas that in the radial direction is reduced. The final macrosegregation formed in the mold rotating at moderate angular velocities appears to be favorable in comparison with the stationary casting, in that not only relatively homogenized composition is achieved, but also a severely positive-segregated channel is restrained.