Papers by Author: M.D. Dupouy

Abstract: This paper presents a method aimed at controlling free surface flow and stirring melt via a magnetic field induced by the permanent magnets. The rotating magnetic field (RMF) can realize the free surface shape control and the melt stirring simultaneously. Numerical model was built to analyse the magnetic field distribution. Two drivers that have the same structure were analysed and optimised. Quasi-steady-state free surface was obtained by regulating the rotating velocity of the magnetic drivers, which is proportional to the magnetic force. Solidification experiment was preformed on a platform of a mini-continuous caster. The solidifying front was observed via addition of a small quantity of Sn-wt.43%Pb into the continuous casting alloy Sn-wt.3.5%Pb, it was found that the solidifying shell grows uniformly under the condition of a proper imposition of the double-permanent-magnet-driver.

Abstract: The main objective of the research project of the European Space Agency (ESA) - Microgravity Application Promotion (MAP) programme entitled Columnar-to-Equiaxed Transition in SOLidification Processing (CETSOL) is the investigation of the formation of the transition from columnar to equiaxed macrostructure that takes place in casting. Indeed, grain structures observed in most casting processes of metallic alloys are the result of a competition between the growth of several arrays of dendrites that develop under constrained and unconstrained conditions, leading to the CET. A dramatic effect of buoyancy-driven flow on the transport of equiaxed crystals on earth is acknowledged. This leads to difficulties in conducting precise investigations of the origin of the formation of the equiaxed crystals and their interaction with the development of the columnar grain structure. Consequently, critical benchmark data to test fundamental theories of grain structure formation are required, that would benefit from microgravity investigations. Accordingly, the ESA-MAP CETSOL project has gathered together European groups with complementary skills to carry out experiments and to model the processes, in particular with a view to utilization of the reduced-gravity environment that will be afforded by the International Space Station (ISS) to get benchmark data. The ultimate objective of the research program is to significantly contribute to the improvement of integrated modelling of grain structure in industrially important castings. To reach this goal, the approach is devised to deepen the quantitative understanding of the basic physical principles that, from the microscopic to the macroscopic scales, govern microstructure formation in solidification processing under diffusive conditions and with fluid flow in the melt. Pertinent questions are attacked by well-defined model experiments on technical alloys and/or on model transparent systems, physical modelling at microstructure and mesoscopic scales (e.g. large columnar front or equiaxed crystals) and numerical simulation at all scales, up to the macroscopic scales of casting with integrated numerical models.

Abstract: The specific objective of the paper is to investigate the effect of fluid flow on the development of a dendritic microstructure and more particularly on the columnar and equiaxed solidification regimes. A gradient furnace (BATMAF) with a possibility of applying a travelling magnetic field was designed for the solidification of aluminium-based alloys. The travelling magnetic field (TMF) drives a forced flow in the liquid above the solidifying interface. Some experiments are achieved in this furnace on an Al-Ni3.5wt% refined alloy. As a result, a significant change of the microstructure due to the transversal melt flow is observed. This work is performed in the framework of the CETSOL/MICAST Microgravity Application Projects of the European Space Agency (ESA).

Abstract: The MICAST research program focuses on a systematic analysis of the effect of convection on the microstructure evolution in cast Al-alloys. The experiments of the MICAST team are carried out under well defined thermally and magnetically controlled, convective boundary conditions and analyzed using advanced diagnostics and theoretical modeling, involving phase field simulation, micro-modeling and global simulation of heat and mass transport. The MICAST team uses binary, ternary and technical alloys of the Al-Si family. This paper gives an overview on recent experimental results and theoretical modelling of the MICAST team.