Influences of dendrite morphologies and solid-back diffusion on macro segregation in directionally solidified blade-like casting.

A newly proposed solidification transport process (STP)-based micro-/macrosegregation model is used to investigate the influences of dendrite morphologies and solid-back diffusion (SBD) on macrosegregation behaviors in dendrite solidification of shaped castings. Via a unified micro-scale parameter, an arbitrary solidifying dendrite structure is reconstructed through the scalar production of a solid-fraction-dependent weighting coefficient vector and basic geometrical vector consisted of spherical, cylindrical, plate-like, inward cylindrical and inward spherical components. Computations are carried out on directionally solidified blade-like Al-4.5wt.%Cu castings with assumed different solid-diffusion-coefficients varying in eight orders of magnitude and different solid-phase morphologies including the five basic geometrical shapes and assumed equiaxed/colummar dendrites and granulated structures. The calculated results comparisons show that a solidification structure with a convex solid-liquid (S/L) interface tends to lighten the macrosegregation formation though the influences of the solid-phase morphologies on macrosegregation behaviors are less significant than that of solid-diffusion-coefficients. (C) 2002 Elsevier Science B.V. All rights reserved.