Modeling of solute redistribution in the mushy zone during solidification of aluminum-copper alloys
Tóm tắt
A mathematical model has been established to predict the formation of macrosegregation for a unidirectional solidification of aluminum-copper alloys cooled from the bottom. The model, based on the continuum formulation, allows the calculation of transient distributions of temperature, velocity, and species in the solidifying alloy caused by thermosolutal convection and shrinkage-induced fluid flow. Positive segregation in the casting near the bottom (inverse segregation) is found, which is accompanied by a moving negative-segregated mushy zone. The effects of shrinkage-induced fluid flow and solute diffusion on the formation of macrosegregation are examined. It is found that the redistribution of solute in the solidifying alloy is caused by the flow of solute-rich liquid in the mushy zone due to solidification shrinkage. A higher heat-extraction rate at the bottom increases the solidification rate, decreasing the size of the mushy zone, reducing the flow of solute-rich liquid in the mushy zone and, as a result, lessening the severity of inverse segregation. Comparisons between the theoretical predictions from the present study and previous modeling results and available experimental data are made, and good agreements are obtained.
Tài liệu tham khảo
M.C. Flemings:Solidification Processing, McGraw-Hill, Inc., New York, NY, 1974, pp. 214–58.
K.M. Fisher:PCH, PhysicoChem. Hydrodyn., 1981, vol. 2, pp. 311–26.
E. Scheil:Metallforschung, 1947, vol. 2, pp. 69–75.
J.S. Kirkaldy and W.V. Youdelis:Trans. TMS-AIME, 1958, vol. 212, pp. 833–40.
M.C. Flemings and G.E. Nereo:Trans. TMS-AIME, 1967, vol. 239, pp. 1449–61.
M.C. Flemings, R. Mehrabian, and G.E. Nereo:Trans. TMS-AIME, 1968, vol. 242, pp. 41–49.
M.C. Flemings and G.E. Nereo:Trans. TMS-AIME, 1968, vol. 242, pp. 50–55.
H. Kato and J.R. Cahoon:Metall. Trans. A, 1985, vol. 16A, pp. 579–87.
I. Ohnaka and M. Matsumoto:Tetsu-to-Hagané (J. Iron Steel Inst. Jpn.), 1987, vol. 73, pp. 1698–1705.
I. Ohnaka and M. Matsumoto:Trans. Iron Steel Inst. Jpn., 1986, vol. 26, pp. 781–89.
W.D. Bennon and F.P. Incropera:Int. J. Heat Mass Transfer, 1987, vol. 30, pp. 2161–70.
W.D. Bennon and F.P. Incropera:Int. J. Heat Mass Transfer, 1987, vol. 30, pp. 2171–87.
C. Beckermann and R. Viskanta:PCH, PhysicoChem. Hydrodyn., 1988, vol. 10, pp. 195–213.
D.G. Neilson and F.P. Incropera:Int. J. Heat Mass Transfer, 1991, vol. 34, pp. 1717–32.
K.C. Chiang and H.L. Tsai:Int. J. Heat Mass Transfer, 1992, vol. 35, pp. 1763–70.
K.C. Chiang and H.L. Tsai:Int. J. Heat Mass Transfer, 1992, vol. 35, pp. 1771–78.
P.C. Carman:Trans. Inst. Chem. Eng., 1937, vol. 15, pp. 150–66.
K. Kubo and R.D. Pehlke:Metall. Trans. B, 1985, vol. 16B, pp. 359–66.
G.S. Beavers and E.M. Sparrow:J. Appl. Mech., 1969, vol. 36, pp. 711–14.
J. Ni and C. Beckermann:Transport Phenomena in Material Processing, M. Charmichi, M.K. Chyu, Y. Joshi, and S.M. Walsh, eds., ASME HTD, Fairfield, NJ, 1990, vol. 32, pp. 45–56.
S.V. Patankar:Numerical Heat Transfer and Fluid Flow, Hemisphere. New York, NY, 1980, pp. 96–102.
K.C. Chiang: Ph.D. Thesis, University of Missouri-Rolla, Rolla, MO, 1990.
R.D. Pehlke, A. Jeyarajan, and H. Wada:Summary of Thermal Properties for Casting Alloys and Mold Materials, Report No. PB83-211003, National Technical Information Service, Washington, DC, 1983, pp. 81-93.