CONVECTIVE-TRANSPORT PHENOMENA AND MACROSEGREGATION DURING SOLIDIFICATION OF A BINARY METAL ALLOY .1. NUMERICAL PREDICTIONS

A continuum model is used to simulate transient convective transport p henomena numerically during solidification of a Pb-19 percent Sn alloy in an experimental test cell. Solidification occurs in an axisymmetri c, annular mold of stainless steel, cooled along its outer vertical wa ll. Results show that, during early stages of solidification, double-d iffusive 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 know n as A-segregates. During intermediate stages of solidification, solut ally driven natural convection spawns a cone segregate in the interior region of the ingot. The final macrosegregation pattern is characteri zed, in general, by increasing Sn concentration with increasing height throughout the ingot and by increasing Sn concentration with decreasi ng radius in the upper portion of the ingot.