1 Center for Advanced Solidification Technology, Shanghai University, Shanghai 200444, China 2 School of Materials and Metallurgy, University of Science and Technology Liaoning, Anshan 114051, China
Cite this article:
ZHU Rui, WANG Junjie, ZHANG Yunhu, TIAN Zhichao, MIAO Xincheng, ZHAI Qijie. Flow and Solidification Microstructure in Metal Melts Driven by a Combined Magnetic Field. Acta Metall Sin, 2024, 60(2): 231-246.
In recent years, solidified structures in metal alloys driven by combined electromagnetic fields have received considerable attention. In this study, the effect of combined magnetic field (CMF) formed by pulsed magneto oscillation (PMO) and static magnetic field on the melt flow of Ga-20%In-12%Sn (mass fraction) and solidification structure of Al-7%Si alloy was investigated. Results of numerical simulations and flow experiments show that the flow pattern is single rolled in the direction parallel to the static magnetic field and double rolled in the direction perpendicular to the static magnetic field, which is different from the double-rolled flow pattern of the melt when the PMO is activated alone. The distribution and evolution of the electromagnetic forces in the melt under CMF are numerically simulated to explain the formation of the flow pattern. Moreover, the experimental results of solidification show that the grain size of the CMF-treated Al-7%Si alloy is smaller than that obtained when PMO is applied. Finally, the grain refinement mechanism of the Al-7%Si alloy under the influence of electromagnetic fields is discussed in relation to the effects of induced currents, electromagnetic forces, and forced flow based on the previously proposed mechanism of grain refinement in solidified metals driven by electromagnetic fields.
Fund: National Natural Science Foundation of China(U1760204);National Natural Science Foundation of China(51974183);Central Guidance on Local Science and Technology Development Fund of Ningxia(2022FRD05007)
Corresponding Authors:
ZHANG Yunhu, associate professor, Tel: 18701896409, E-mail: yunhuzhang@shu.edu.cn; MIAO Xincheng, professor, Tel: 15541217108, E-mail: miaoxincheng@ustl.edu.cn
Fig.1 Schematic of magnetic field measurement setup (h1 and T1 are the height and width of the magnet, respectively; L0is the distance from the magnet to the outer diameter of the coil; H1 and D1 are the height and diameter of the coil, respectively; PMO—pulsed magneto-oscillation)
Fig.2 Waveform of employed PMO (Ip, tp, and f are the peak current, pulse width, and frequency of PMO current, respectively; I—current density; t—time)
Fig.3 Schematic of melt flow measurement setup (H0 and D0 are the height and diameter of the cylindrical container respectively; H2 is the melt height; h is the distance between the bottom of the container and the bottom of the coil; UDV—ultrasound Doppler velocimetry; P1 is the position of the probe at the bottom of the container)
Thermophysical property
Al-7%Si
Ga-20%In-12%Sn
Unit
Liquidus TL
615
10.5
oC
Density ρ
2422
6360
kg·m-3
Viscosity υ
0.5 × 10-6
0.34 × 10-6
m2·s-1
Electrical conductivity σ
3.74 × 106
3.27 × 106
S·m-1
Relative permeability μr
1
1
-
Relative permittivity εr
1
1
-
Table 1 Thermophysical properties of Al-7%Si (mass fraction) and Ga-20%In-12%Sn alloys[7]
Fig.4 Numerical simulation geometries of PMO (a) and CMF (b) (CMF—combined magnetic field)
Fig.5 Measured static magnetic field distributions (The two numbers adjacent the up and down arrows in the label are the maximum and minimum values, respectively, the same below)
Fig.6 Measured Bx, By,and Bz (a) and comparison of measured and simulated magnetic field strength along the z direction (b) at the center of the coil under the application of PMO (Ip = 1500A, f = 30 Hz, tp = 3 ms)
Fig.7 Comparison of measured and simulated results of the crests and troughs of Bz along the center axis of the coil under the application of PMO (Ip= 1500A, f = 30 Hz, tp= 3 ms)
Fig.8 Magnetic field distributions in the melt at 0.25tpunder the application of different magnetic fields
Fig.9 Melt flow of Ga-20%In-12%Sn under the impact of PMO (Ip= 1500 A，f = 30 Hz，tp= 3 ms)
Fig.10 Melt flow under the application of CMF
Fig.11 Solidification microstructures of Al-7Si alloy treated by PMO (a, b) and CMF (c, d) with different current peaks (a, c) 2000 A (b, d) 2500 A
Fig.12 Lorentz force (F) distributions in the xz-plane under the application of PMO
Fig.13 Lorentz force distributions in the xz-plane under the application of CMF
Fig.14 Variations of melt average flow velocity () with time under the application of PMO (a) and CMF (b)
Fig.15 Relationship between the flow velocity Uz and Fz at point P under the application of CMF (a) and its enlarged view of the dotted box in Fig.15a (b)
Fig.16 Induced electric current (J) distributions in the melt under the application of PMO (a) and CMF (b) with current peak of 2500 A
Fig.17 Schematics of magnetic field direction, induced electric current direction, and induced electric current loop area (SP and SC are the areas of the induced current loop under the application of PMO and CMF, respectively )
Fig.18 Lorentz force distributions in the melt under the application of PMO (a) and CMF (b) with current peak of 2500 A
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