Thermo-inelastic simulation of butt curl phenomena during DC casting of aluminum

In an aluminum DC casting slab, butt curl phenomena are recognized at the short side of its bottom region and they are prone to decrease the productivity through fatal defects such as hot cracking or metal bleeding. In order to evaluate the mechanism of butt curl growth, a thermo-mechanical finite element model has been developed, in which thermally induced strains and stresses associated with phase transformation (solidification phenomena) are simulated using an elasto-plastic constitutive equation based on an isotropic hardening rule and the Mises yield condition. Comparison of butt curls shows a good agreement between calculations and measurements within tolerance of ± 20 %. As a driving force of butt curl, it is found that a torque moment due to tensile stresses distributing along a mushy region makes the solidified bottom shell bent rapidly when the whole slab surface is covered with secondary coolant. The study on influence of casting condition on butt curl growth reveals that resultant variations of butt curl are almost consistent with practical experiences in the cast house.