Revealing the influence of high magnetic field on the solute distribution during directional solidification of Al-Cu alloy

doi:10.1016/j.jmst.2021.01.058

Abstract

Abstract:

The effect of the high magnetic field (MF) on the distribution of solute concentration during directional solidification of Al-Cu alloy under low growth speed was experimentally investigated. The amount of non-equilibrium eutectic is quantified via X-ray computed tomography (XCT) and demonstrated to reduce with the application of MF. Further, experimental results reveal that the MF alleviates the microsegregation and increases the average Cu concentration in solid solution, leading to the increases of the effective partition coefficient ke. It was also found that Cu concentration in solid solution increases continuously with the increasing intensity of MF, following the strengthening of micro-hardness. The change of ke under the MF is demonstrated to attribute to the thermoelectric magnetic convection (TEMC) in the mushy zone and the thermoelectric magnetic force (TEMF) acting on the solid. The TEMC is supposed to cause secondary convection owing to the inequality in flow velocities of circulation in different positions of dendrite stem. And the vacancies created by the proliferation and movement of dislocations induced by TEMF in the matrix is supposed to be able to capture solute atoms and thus enhance the solute concentration in the solid solution.

Key words: Microsegregation, Cu concentration, Partition coefficient, Magnetic field, Directional solidification

Pengchuan Wang, Sansan Shuai, Chenglin Huang, Xin Liu, Yanan Fu, Jiang Wang, Zhongming Ren. Revealing the influence of high magnetic field on the solute distribution during directional solidification of Al-Cu alloy[J]. J. Mater. Sci. Technol., 2021, 88: 226-232.

Figures/Tables 7

Fig. 1. Morphologies near the solid/liquid interface in the directional solidified Al-10 wt.%Cu (a1-d1) and Al-4 wt.%Cu (a2-d2) alloys under different MFs at a pulling rate of 1 μm s-1: (a) 0 T, (b) 1 T, (c) 3 T, (d) 5 T.

Fig. 2. 3D reconstruction images of the non-equilibrium eutectics of directional solidified Al-10 wt.%Cu (a1-d1) and Al-4 wt.%Cu (a2-d2) alloys under different MFs at a pulling rate of 1 μm s-1: (a) 0 T, (b) 1 T, (c) 3 T, (d) 5 T; (e) the variation of the volume fraction of non-equilibrium eutectics with different MF.

Fig. 3. Contour maps of Cu concentration in the transverse sections of directionally solidified Al-10 wt.%Cu (1) and Al-4 wt.%Cu (2) alloys under different MF at a pulling rate of 1 μm s-1: (a) 0 T; (b) 1 T; (c) 3 T; (d) 5 T; (e) Cu concentration versus solid fraction proﬁles in the transverse sections of directionally solidiﬁed Al-Cu alloy under different MF.

Fig. 4. (a) the Cu concentration in solid solution of directionally solidified Al-Cu alloy under different MF; (b) the microhardness of directionally solidified Al-Cu alloy under different MF.

Fig. 5. Relationship between effective partition coefﬁcient and the MF intensity for Al-10 wt.%Cu and Al-4 wt.%Cu alloys during directional solidiﬁcation.

Fig. 6. The schematic diagrams showing the migration of Cu atoms in mushy zone(a) and Cu atoms trapped by vacancies (b).

Fig. 7. TEM bright field images of directionally solidified Al-4 wt.%Cu alloy under different MF: (a1) 0 T, (a2) 5 T; HRTEM images of Al-10 wt.%Cu alloy under different MF: (b1) 0 T, (b2) 5 T; TEM images with high magnification in the dual-beam diffraction of Al-10 wt.%Cu alloy under different MF: (c1) 0 T, (c2) 5 T.

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