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Sino-German Workshop on Electromagnetic Processing of Materials,

Sino-German Workshop on Electromagnetic Processing of Materials, 11.10 – 13.10.2004 Shanghai, PR China Use of magnetic fields during solidification under microgravity conditions J.Dagner, M.Hainke, J.Friedrich, G.M ü ller Outline:

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Sino-German Workshop on Electromagnetic Processing of Materials,

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  1. Sino-German Workshop on Electromagnetic Processing of Materials, 11.10 – 13.10.2004 Shanghai, PR China Use of magnetic fields during solidification under microgravity conditions J.Dagner, M.Hainke, J.Friedrich, G.Müller Outline: • The conservation equations utilizing the volume averaging technique • Models for time dependent magnetic fields • Influence of forced flows on the solidification process Contract no. 14347/00/NL/SH Contract no. 50WM0042

  2. Microgravity – Is it necessary? Objectives of MICAST (The effect of magnetically controlled fluid flow on microstructure evolution in cast technical Al-alloys): Systematic analysis of the influence of convection on • the evolution of the mushy zone • micro- and macro segregation • morphology of dendrites in binary AlSi, ternary AlSiMg and technical A357 alloys. Diffusive and controlled convective conditions are achieved by using microgravity environment and time-dependent magnetic fields, i.e. rotating magnetic fields (RMF). Schematic of dendrites solidifying under the influence of convection MICAST - MAP Project No. AO-99-031

  3. G=4K/mm T Directional solidification with time dependent magnetic fields applied • Modeling of (global) heat transfer and macrosegregation • Solidification of binary AlSi7 and ternary AlSi7Mg0.6 cast alloys • Influence of rotating and traveling magnetic fields on the solidification process Heat flux z AlSi7 Melt flow Bulk liquid Mushy zone Vg= 0,1mm/s Solid d=8mm The software package CrysVUn Condition for directional solidification

  4. solid mush liquid The volume averaging technique1 For a quantity  in the phase k (k= solid or liquid) the volume average is defined: The fraction of phase k is: The intrinsic volume average: Mixture concentration within the REV: Macrosegregation: solid liquid Representative elementary volume (REV) 0 ; Ts=Tl=T; REV Solidifying alloy sample with one of the REV inside the mushy zone (marked) [1] Poirier et al. Met. Trans. B. 22 889-900 (1991)

  5. z z l T Interdendritic convection is causing macrosegregation As Pr<<Sc the concentration field is changed at much smaller flow velocities than the temperature field. Phase diagram z Local solute enrichment due to upwards directed flow. flow MZ Convective parameter C <0 negative macrosegregation 0<<1 positive macrosegregation >1 remelting Axial temperature, liquid concentration and liquid volume fraction during directional solidification.

  6. Model2 for directional alloy solidification Energy conservation Convective term causing macrosegregation Species conservation For ternary systems: Plain liquidus surface for primary solidification with isothermal binary valleys Phase diagram relation Momentum conservation Lorentz – force vector Mass conservation [2] Poirier et al. Met. Trans. B. 22 889-900 (1991)

  7. Time dependent magnetic fields Rotating Magnetic Field [3]: Principal action of the Lorentz-force generated by a magnetic field rotating around the axis of a cylindrical melt volume Lorentz-force: Taylornumber : Lorentz-force Secondary flows in meridonal plane occur on bottom and top in a finite cylinder geometry Flow field (r: azimuthal, l: meridonal) [3] B. Fischer et al., Proc. EPM 2000, 497-502 (2000)

  8. t+t t z Bz  r Br Time dependent magnetic fields Traveling Magnetic Field [4]: A single axisymmetric harmonic magnetic wave traveling in z direction Lorentz –force: Taylor number: z r Flow field with fl pointing downward Lorentz-force [4] K. Mazuruk, Adv. Space Res. 29,4,541-548 (2002)

  9. Mushy zone Directional solidification of AlSi7 applying RMF B0=2mT vg=0.1mm/s, Gl=4K/mm Vmax = 3.2x10-4 m/s Cmix=8.28wt.% Symmetry axis Channel formation Te=850K Mixture concentration Streamlines for meridonal flow Azimuthal flow Liquid fraction Experimental result from DLR, Cologne Hainke, Friedrich, Müller; J. Mat. Sci., 2004

  10. RMF applied to the solidification of a ternary alloy Comparison between the macrosegregation caused by the forced fluid flow for a binary (AlSi7) and a ternary (AlSi7Mg0.6) Aluminum alloy. Extension of mushy zone AlSi7: 37 K AlSi7Mg0.6: 60 K

  11. Comparison of the macrosegregation due to TMF and RMF for AlSi7 Resulting macrosegregation for RMF or TMF applied to the solidification of a binary AlSi7 alloy. Left part: stream function; right part: liquid fraction (d=0.05). The arrow indicates the direction of the Lorentz-force. Dagner, Hainke, Friedrich, Müller; EPM, 2003

  12. Conclusions • Depending on field configuration and strength, macrosegregation is observed in calculations and experiment even in small samples for AlSi7 and AlSi7Mg0.6 Alloys • The differences in the resulting macrosegregation between AlSi7 and AlSi7Mg0.6 within the used model are negligible. Thus AlSi7Mg0.6 can be treated as a binary mixture • The calculations suggested that using TMF will lead to a more pronounced effect than in the case of RMF • When TMF is used, the direction of the Lorentz-force represents a additional process parameter influencing macrosegregation

  13. Acknowledgements Prof. Dr. L. Ratke and S. Steinbach (Institute for Space Simulation, DLR, Cologne) for the experimental results obtained with the ARTEMIS and the ARTEX facilities. This work was financially supported by the DLR under contract no. 50WM0042 and by ESA under contract no. 14347/00/NL/SH within the framework of the European research project MICAST (ESA MAP AO-99-031). http://www.cgl-erlangen.com

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