1. NUMERICAL STUDY OF THE INFLUENCE OF AN APPLIED ELECTRICAL POTENTIAL ON THE SOLIDIIFCATION OF A BINARY METAL ALLOY P.A. Nikrityuk, K. Eckert, R. Grundmann Institute for Aerospace Engineering, Dresden University of Technology, Germany 2 nd Sino-German Workshop on Electromagnetic Processing of Materials October 16-19, 2005, Dresden, Germany SFB 609

2. Historical preamble of a pulse electric discharging (PED) in metallurgy The goal of PED is the modification of the microstructure during solidification A. Mirsa (Metal. Trans. A, 1985, 1986) - Pioneering publication about en experimental study of DC passing though the solidified melt. Grain size refinement was reported. M. Nakada et al (ISIJ Int., 1990) - Detailed experimental study of the PED impact on Sn15wt%Pb alloy solidification. Hypothesis: the Lorentz force (Pinch force) is responsible for the grain refinement through mechanical shearing of dendrites. A. Prodhan et al (Met. Mat. Trans.B, 2001) – Experimental study of solidification of Aluminum in electric field. The reduction of pinhole porosity and columnar-to- equiaxed transition was reported by application DC and 50 Hz AC. M. Gao et al (Mat. Sci Eng. A, 2002) – Experimental study of the ZA27 alloy solidification treated with PED. Modification of the dendrite grain size from larges to the smaller was reported. SFB 609

3. Historical preamble of a pulse electric discharging (PED) in metallurgy The goal of PED is the modification of the microstructure during solidification A. Mirsa (Metal. Trans. A, 1985, 1986) - Pioneering publication about en experimental study of DC passing though the solidified melt. Grain size refinement was reported. M. Nakada et al (ISIJ Int., 1990) - Detailed experimental study of the PED impact on Sn15wt%Pb alloy solidification. Hypothesis: the Lorentz force (Pinch force) is responsible for the grain refinement through mechanical shearing of dendrites. A. Prodhan et al (Met. Mat. Trans.B, 2001) – Experimental study of solidification of Aluminum in electric field. The reduction of pinhole porosity and columnar-to- equiaxed transition was reported by application DC and 50 Hz AC. M. Gao et al (Mat. Sci Eng. A, 2002) – Experimental study of the ZA27 alloy solidification treated with PED. Modification of the dendrite grain size from larges to the smaller was reported. SFB 609

4. Historical preamble of a pulse electric discharging (PED) in metallurgy The goal of PED is the modification of the microstructure during solidification A. Mirsa (Metal. Trans. A, 1985, 1986) - Pioneering publication about en experimental study of DC passing though the solidified melt. Grain size refinement was reported. M. Nakada et al (ISIJ Int., 1990) - Detailed experimental study of the PED impact on Sn15wt%Pb alloy solidification. Hypothesis: the Lorentz force (Pinch force) is responsible for the grain refinement through mechanical shearing of dendrites. A. Prodhan et al (Met. Mat. Trans.B, 2001) – Experimental study of solidification of Aluminum in electric field. The reduction of pinhole porosity and columnar-to- equiaxed transition was reported by application DC and 50 Hz AC. M. Gao et al (Mat. Sci Eng. A, 2002) – Experimental study of the ZA27 alloy solidification treated with PED. Modification of the dendrite grain size from larges to the smaller was reported. SFB 609

5. Problem formulation macroscale electric current density is homogeneous microscalemesoscale SFB 609 R 0 =25 mm, H 0 =75 mm

6. Problem formulation macroscale electric current density is homogeneous microscalemesoscale SFB 609 R 0 =25 mm, H 0 =75 mm micro- and mesoscale electric current density is NOT homogeneous

7. Macro-energy transport during Sn15wt%Pb solidification by DC application SFB 609 Steady DC from 50 s to 80 s during UDS

8. Macro-energy transport during Sn15wt%Pb solidification by DC application SFB 609 Periodic DC with period “on and off ” 1 sec Steady DC from 50 s to 80 s during UDS Joule heating is reduced !!!!!

9. DC is switch on after 30 sec and switched off after 60 sec 0.1V, 4672 A Volume fraction of the liquidTemperature SFB 609

10. Joule heating effect SFB 609 Joule heating in the liquid phase >> Joule heating in the solid phase

11. Axial profiles of the temperature and the electric potential at t = 70 sec SFB 609 solid liquid

12. Axial profiles of the temperature and the electric potential at t = 70 sec SFB 609 Analytic model – Nikrityuk et al, 2005, Wiley-VCH Verlag solid liquid

13. Mesoscale consideration SFB 609 R d =10 -4 m V s =10 -4 m/s E=1-30 V/m Electroconducting non-homogeneous media, Nikrityuk et al, Met. Mat. Trans, 2005, submitted

14. Spatial distribution of electric potential, current density and Joule heating SFB 609 electric potentialcurrent density Joule heating

15. Spatial distribution of the velocity field SFB 609

16. Spin-up of the interdendritic liquid SFB 609 Nikrityuk et al, Phys Fluids, 2005 Time scale of spin-up is 10 -3 sec !!!!

17. Conclusions Application of PED perpendicularly to the solidification front lead to a much stronger heating of the liquid phase in comparison to the solid phase (the heating is caused by the Joule heating effect) A shorter duration of PED decrease of the Joule heating of the melt The inhomogeneity of the electrical current in the mushy zone induces a Lorentz force (pinch force), which induces a toroidal vortex near the dendrite tip. This convection may lead to the accumulation of solute at the dendrite tip and obstruction of the columnar grain growth (Martorano et al, 2003, Willers et al 2005, Eckert et al 2005) The spin-up time of the vortex has order of O(10 -3 ) sec for E z of order O(10) V/m Models proposed to use Macroscale level: a variant of the mixture model (Stefanescu, 1996) Microscale level: Phase-field model (Karma 1996, Beckermann, 1999) SFB 609

18. Cited publications P.A. Nikrityuk, M. Ungarish, K. Eckert, R. Grundmann. “Spin-up of a liquid metal flow driven by a rotating magnetic field in a finite cylinder. A numerical and analytical study“ Phys. Fluids 17, 2005, 067101-1-016 P.A. Nikrityuk, K. Eckert, R. Grundmann. “Numerical study of the influence of a rotating magnetic field on unidirectional solidification of a binary metal alloy”, I.J.Heat and Mass Transfer, in press, 2005 P.A. Nikrityuk, K. Eckert, R. Grundmann. “Rotating magnetic field driven flows in conducting inhomogeneous media. Part I: Numerical Study“, submitted to Metallurgical and Materials Transactions B, 2005 P. A. Nikrityuk, K. Eckert, R. Grundmann. Proceeding of Continuous Casting Conf., Wiley-VCH Verlag, pp. 1-14, 2005. S. Eckert, B. Willers, P. Nikrityuk, K. Eckert, U. Michel, G. Zouhar. Application of a rotating magnetic field during directional solidification of Pb-Sn alloys: Consequences on the CET. Mat. Sci. Eng. A, in press, 2005. Dr. YANG “Microstructure evolution of semi-solid magnesium alloy AZ91D under electric current” Dr. PAN “Impose of electric field on crystallization of metallic amorphous” Proposed partners from China SFB 609