Two-phase modelling of hot tearing in aluminium alloys using a semi-coupled approach

Hot tearing, one of the most severe defects observed in castings, is due to both tensile stresses and lack of interdendritic liquid feeding in the mushy zone. In order to predict this phenomenon, the two-phase averaged conservation equations for mass and momentum must be solved in the mushy region of the material. In recent contributions, M’Hamdi et al (2002 Metall. Mater. Trans. A 33 2081–93) proposed a strongly coupled resolution scheme for this set of equations. The solution of the mechanical problem is obtained using a rheological model established by Ludwig et al (2005 Metall. Mater. Trans. A 36 1525–35). In the present contribution, the problem is addressed with a slightly different approach. The same rheological model is used for the solid skeleton (i.e. saturated porous medium treatment), but the influence of liquid pressure is neglected at this stage. This assumption allows for a weakly coupled resolution scheme in which the mechanical problem is first solved alone using ABAQUS® and user subroutines. Then, the liquid pressure is calculated separately accounting for the viscoplastic deformation of the porous solid and solidification shrinkage. This is done with a code previously developed for porosity calculations which uses a refined mesh in the mushy zone (Pequet et al 2002 Metall. Mater. Trans. A 33 2095–106). The stability of the numerical tools is presented and the modelling approach is then applied to a virtual experiment. Finally, two approaches are examined to study the hot tearing tendency in this problem.