Prediction of internal cracking in a direct-chill cast, high strength, Al–Mg–Si alloy

In order to develop a new method for predicting the internal cracking in direct-chill (DC) cast billets, tensile tests of the mushy zone of high-strength Al–Mg–Si alloys were undertaken, and solidification and thermal stress simulations of the DC casting process were performed. In this study, the solidification process was calculated using a commercial solidification package, CAPFLOW and the thermal stress was analysed with a structural analysis package, ANSYS. The thermal histories from CAPFLOW were used as input data to an elasto-plasticity model which simulated the thermal stress and deformation of the billet during the casting process. Prediction of the internal cracking in the DC billet was carried out by comparing the equivalent plastic strain obtained from the elasto-plasticity thermal deformation analysis with the fracture strain of the alloy obtained by high-temperature tensile tests. The analysis results in the mushy zone show that the equivalent plastic strain is an important factor in the occurrence of internal cracking: when the equivalent plastic strain exceeds the fracture strain of the alloy, the billet will crack, and the predictions obtained by this method are in good agreement with the experimental results.