Étude de l'effet des mouvements de convection sur les structures de solidification et ségrégations de l'alliage d'aluminium 5182

Abstract : In order to understand the influence of convection on the formation of solidification structures and segregations in 5182 Aluminium alloy, billets of this alloy were cast at Centre de Recherche de Voreppe (ALCAN-Péchiney). The billets were 76 mm in diameter and cast in a semi-continuous system. The mould was inserted into an inductor generating an electromagnetic field which permits the stirring of the melt. The stirring was applied either in the direction of the natural convection, or in the reverse direction. Four intensities were used. The effect of grain refining and superheat was also studied. The billets obtained were refined or not, cast with high superheat (35°C - 40°C) or low superheat (15 - 30°C), and were stirred directly or inversely with the four stirring intensities, applied successively during the casting. The results showed that the different parameters used have some influence on the temperature profiles, on the billet structure and on the microsegregation profiles. In the case of stirred and non refined billets, it was observed that the temperature profiles present an isothermal plateau around the liquidus temperature. In the case of stirred and refined billets, the isothermal plateau was at 2.5°C of undercooling. This plateau was associated with the transport and growth of the solid. The observations of the billet structure show the presence of bands of columnar grains alternated with bands of equiaxed grains, in the case of stirred and non grain refined billets. These bands were explained using a GV diagram, considering the growing time of the columnar and equiaxed grains, and the transport time of the equiaxed grains. In the case of grain refined billets, the structure observed is formed of dendritic and/or globulitic grains. It was observed that the extent of globulitic grains increased when the stirring intensity increased ; it was also observed that the grain size decreased when the stirring increased even with grain refined billets. Results show a decrease of grain size with low superheat. The microsegregation profiles show an influence of the stirring via the structure of the billet. It was observed that for the dendritic structure, the microsegregation profiles present a negative curvature which becomes positive when the extent of the globulitic grains increases.
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Theses
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http://docnum.univ-lorraine.fr/prive/INPL_T_2004_SFERDJELLA_S.pdf
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Submitted on : Thursday, March 29, 2018 - 12:37:06 PM
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Sabrina Sferdjella. Étude de l'effet des mouvements de convection sur les structures de solidification et ségrégations de l'alliage d'aluminium 5182. Autre [cond-mat.other]. Institut National Polytechnique de Lorraine, 2004. Français. ⟨NNT : 2004INPL078N⟩. ⟨tel-01750070⟩

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