Improving the Solidified Structure by Optimization of Coil Configuration in Pulsed Magneto-Oscillation

doi:10.1007/s40195-018-0799-0

Abstract

Abstract:

Using both numerical and experimental methods, we studied the effect of coil configuration of pulsed magneto-oscillation (PMO) on distribution of electromagnetic field, flow field and solidification structure with the same pulse current parameters in Al ingots. We designed and constructed three types of coils: surface pulsed magneto-oscillation, hot-top pulsed magneto-oscillation (HPMO) and combined pulsed magneto-oscillation (CPMO). PMO treatment refined the solidification structure in all the ingots. The configuration of the PMO, however, introduced differences in magnetic field intensity, electromagnetic force, Joule heat, flow field, equiaxed grain zone, grain size and growth direction of columnar grains. The largest equiaxed grain zone was found in CPMO treated ingot, and the smallest grain size was found in both HPMO and CPMO treated ingots. Numerical simulation indicated that difference in electromagnetic field and flow field resulted in differences in solidification structure. HPMO is more advantageous over others for large ingot production.

Key words: Pulsed magneto-oscillation, Coil configuration, Electromagnetic field, Flow field, Solidification structure, Optimization

Jing Zhao, Ji-Hao Yu, Ke Han, Hong-Gang Zhong, Ren-Xing Li, Qi-Jie Zhai. Improving the Solidified Structure by Optimization of Coil Configuration in Pulsed Magneto-Oscillation[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(12): 1334-1344.

Figures/Tables 14

Fig. 1 Procedure of the study

Fig. 2 Coil configurations of PMO

Fig. 3 FEM models used in the simulation: a SPMO; b HPMO; c CPMO

Table 1 Physical parameters of Al melt

Density (kg/m³)	Viscosity (Pa s)	Electrical resistivity (Ω m)	Relative permeability
2375	2.51	2.42?×?10^-7	1

Fig. 4 Variation of pulsed electricity in a coil: a 1/4 period; b 1/2 period; c 3/4 period; d 1 period

Fig. 5 Schematic illustration of experimental setup

Fig. 6 Geometry of the ingot (a) and sampling instruction (b). U0 is the discharge voltage

Fig. 7 Distribution of the magnetic field intensity: a SPMO; b HPMO; c CPMO

Fig. 8 Distribution of electromagnetic force: a SPMO; b HPMO; c CPMO

Fig. 9 Distribution of Joule heat at T/2: a SPMO; b HPMO; c CPMO

Fig. 10 Distribution of flow field: a SPMO; b HPMO; c CPMO

Fig. 11 Solidification structure of Al ingots: a untreated; b with SPMO; c with HPMO; d with CPMO. The dotted line circle marked the equiaxed zone

Table 2 Equiaxed crystal ratio and size of equiaxed grain of Al ingots

	Untreated	SPMO	HPMO	CPMO
Equiaxed crystal ratio	2.5%	37.13%	41.46%	81.3%
Size of equiaxed grain (μm)	1063	377	233	240

Fig. 12 Local solidification structure of Al samples: a untreated; b with SPMO; c with HPMO; d with CPMO. Micrographs taken at the lower half and center axil the ingots. Sample location can be found in Fig. 6

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