TWO-PHASE MODELING OF HOT TEARING IN ALUMINUM ALLOYS USING A SEMI-COUPLED METHOD

摘要

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, it is thus necessary to accurately model both the mechanical behaviour of the solid skeleton and the variation of pressure in the liquid across the mushy zone. In order to meet such requirements, 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. 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. Based on the theory of saturated porous media, these authors captured the compressible and partially cohesive nature of the mushy zone.rnIn the present contribution, the problem is addressed using a slightly different approach. The same rheological model is used for the solid skeleton (i.e. saturated porous medium treatment) but the liquid pressure drop in the mushy zone is neglected. This assumption allows for a weakly coupled resolution scheme in which the mechanical problem is first solved alone. Then, the liquid pressure is calculated separately accounting for the viscoplastic deformation of the porous solid (i.e. div(v_s) ≠ 0). The latter step is performed using a refined mesh in the mushy zone. This leads to both the prediction of porosity formation and the study of hot tearing formation conditions. Finally, the methodology applicable to experimental validations is presented.