Convective Transport Phenomena and Macrosegregation During Solidification of a Binary Metal Alloy: I—Numerical Predictions

A continuum model is used to simulate transient convective transport phenomena numerically during solidification of a Pb-19 percent Sn alloy in an experimental test cell. Solidification occurs in an axisymmetric, annular mold of stainless steel, cooled along its outer vertical wall. Results show that, during early stages of solidification, double-diffusive convection and liquid exchange between melted and mushy zones are responsible for the formation of channels in the outer periphery of the ingot, which ultimately lead to a form of macrosegregation known as A-segregates. During intermediate stages of solidification, solutally driven natural convection spawns a cone segregate in the interior region of the ingot. The final macrosegregation pattern is characterized, in general, by increasing Sn concentration with increasing height throughout the ingot and by increasing Sn concentration with decreasing radius in the upper portion of the ingot.