The Effect of Fluid Convection on Microstructures of Directionally Solidified Castings

Tien Shou Lei; Wen Shiung Chang; Shyen Yang Dong

doi:10.4028/www.scientific.net/MSF.508.473

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The Effect of Fluid Convection on Microstructures of Directionally Solidified Castings
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In Situ Optical Determination of Fraction Solid of Al-Si-Mg Alloys
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The Effect of Fluid Convection on Microstructures of Directionally Solidified Castings

Abstract:

Fluid convection during solidification of castings will influence the final structures of the castings. A vertical cylindrical casting set-up has been designed to provide two zones of solidification simultaneously with two moving fronts directionally upward and directionally downward, respectively. This two zone directional solidification casting was composed of a cylindrical Furan sand mold with a water chilled center hole block at the center of the casting. Experimentally it was observed that the cooling rates at different locations of the downward zone were much more even than those of the upward one and this is considered to be the result of a more even temperature distribution along the downward front moving zone due to stronger fluid convection. Fluid convection tends to mix up the liquid and results in a more even temperature distribution and a lower degree of segregation of the element molybdenum which has a strong tendency to segregate to the carbide in ductile iron. The characteristics of the matrix microstructure and the growing direction of carbide of this directionally solidified ductile iron has been investigated with SEM and EBSD techniques.