Numerical simulation of macrosegregation during solidification of WE43 (Mg-4.3wt-% Y-2.0wt-% Nd-0.6wt-% Gd) magnesium alloy

摘要

The formation of macrosegregation driven by multicomponent thermosolutal convection during solidification of WE43 magnesium alloy is numerically studied. A two-dimensional solidification model that describes the conservation of mass, momentum, energy and solute is presented. The experiments are performed in the resin sand mould with a graphite chill placed on one side of the cavity. The validation of computer codes is carried out by comparisons with the experimentally measured cooling curves and concentrations. The influences of mould material and characteristic grain size on macrosegregation are numerically investigated. For a total sand mould casting, the magnitude of macrosegregation is reduced, although the solidification rate is slower than that cooled with a graphite chill. Increasing the characteristic grain size not only causes a serious positive segregation but also leads to the formation of channel segregates. The channel segregation occurs thanks to the weak instabilities of the growing front triggered by the fluid flow.