Fracture prediction during sawing of DC cast high strength aluminium alloy rolling slabs

The semicontinuous direct chill (DC) casting of large cross-section rolling sheet ingots of high strength aluminium alloys (2xxx and 7xxx series) gives birth to high residual (internal) stresses generated by a non-uniform cooling. These stresses must be relieved by a thermal treatment in order to be able to safely saw both ingot butt and head. Otherwise, saw pinching or blocking might occur due to the compressive residual stresses, or cut parts might be brutally released by erratic propagation of a crack ahead of the saw groove thus injuring people or damaging equipment. As these high added value ingots must be produced in secure conditions, a better control of the sawing procedure is required, which could allow the suppression of the thermal treatment and therefore save time and energy. By studying the stress build-up during casting and cooling then the stress relief during sawing operations of rolling sheet ingots, key parameters for the control and optimisation of the processing steps can be derived. To do so, the DC casting of the high strength AA2024 alloy is modelled with ABAQUS 6?5 with special attention to the thermomechanical properties of the alloy. The sawing operation is then simulated by removing mesh elements such as to reproduce the progression of the saw in the ingot. Preliminary results showing the stress relief during sawing accompanied by the risk of saw blocking due to compression or initiating a crack ahead of the saw are analysed with an approach based on the rate of strain energy release.