The phenomena responsible for the formation of macrosegregations and grain structures during solidification are closely related. We present a model study of macrosegregation formation in an industrial sized (350 mm thick) direct chill (DC) cast aluminum alloy slab. The modeling of these phenomena in DC casting is a challenging problem mainly due to the size of the products, the variety of the phenomena to be accounted for, and the nonlinearities involved. We used a volume‐averaged two‐phase multiscale model that describes nucleation on grain refiner particles and grain growth, fully coupled with macroscopic transport: fluid flow driven by natural convection and shrinkage, transport of free‐floating equiaxed grains, heat transfer, and solute transport. The individual and combined roles of shrinkage, natural convection, and grain motion on the sump profile and macrosegregation formation are analyzed. The formation and evolution of grains are discussed. We show that it is important to account for all the named transport mechanisms to be able to explain the macrosegregation pattern observed experimentally in DC cast ingots.

The removal of inclusions by flotation in mechanically agitated vessels is widely used in liquid aluminum treatments. Originating from different sources (oxide skins, refractory, or recycling wastes), inclusions may have disastrous repercussions such as deterioration of the physical properties of the cast products or difficulties during forging processes. With the aim of both a better understanding of the physical processes acting during flotation and the optimization of the refining process, a mathematical modeling of the behavior of the population of inclusions has been set up. Transport phenomena, agglomeration of inclusions, and flotation are considered here. The model combines population balance with convective transport of the inclusions, in order to calculate the time evolution of the inclusion size distribution. An operator-splitting technique is employed to solve the coupled population balance equation (PBE) and the transport equation. The transport equation is solved using a finite volume technique associated with a total variation diminishing scheme, whereas the PBE resolution relies on the fixed pivot technique developed by Kumar and Ramkrishna. A laboratory-scale flotation vessel is modeled and the results of a two-dimensional (2-D) simulation are presented.

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.

International audienceIn an induction furnace, as a result of electromagnetic forces, the free surface of a liquid aluminum bath deforms and takes the form of a dome. The oxide layer that forms spontaneously on the free surface of aluminum melts may also influence the deformation by exerting an additional friction force on the metal. A non-intrusive experimental technique-Structured Light Fringe Projection-was used to measure the complete surface deformation and its fluctuations, for a varying set of operating parameters-inductor current intensity and initial liquid metal filling level inside the crucible. For an axisymmetric geometry, numerical simulations were carried out to calculate in a single framework: (i) the electromagnetic forces using the A-V formulation, (ii) the free surface deformation using the Volume of Fluid method, and (iii) the turbulent stirring of the metal using a RANS-based k-omega model. The friction force due to the oxide layer was modeled by imposing a pseudo-wall condition on the free surface, which makes the interfacial velocity very small compared to the average liquid metal pool velocity. A marked impact on the dome height due to applied friction force is observed. Finally, comparisons between the predicted and measured domes are presented

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