Investigation on the Change of Thermoelectric Power of Al-Fe Hypoeutectic Alloy Melt Caused by AC Magnetic Field

Jianfeng ZHANG^{1}, Qing LAN^{2}, Qichi LE^{2}()

1 College of Sciences, Northeastern University, Shenyang 110819, China 2 Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China

A lot of studies have shown that electromagnetic field can significantly refine the metal solidification structure, thus improve the deformation properties and functional performance of metallic materials. However, the mechanism of how electromagnetic field affects melt structure remains unclear, so an intensive study of the effects of electromagnetic field on melt structure is very important for an in-depth understanding of the essence of melt solidification under external electromagnetic field. The effect of alternating current (AC) magnetic field with different exciting currents, magnetic frequencies and loading time on the thermoelectric potential difference (U) and melt microstructure of Al-0.99%Fe (mass fraction) hypoeutectic alloy at different temperatures was investigated in this work. The results showed that AC magnetic field would lead to a decrease in U of liquid Al-0.99%Fe hypoeutectic alloy. When the magnetic field was removed, the decreased thermoelectric potential difference experienced a rapid recovery process and a poor recovery process to increase to the initial value. The influence of AC magnetic field on U was different at different temperatures. With the increase of the magnetic frequency, the influence of AC magnetic field on U decreased. And the influence of AC magnetic field on U increased with the increase of the exciting current and loading time, however, there was a saturated loading time. There was a correlation between the change of U of Al-0.99%Fe hypoeutectic alloy and the change of size of the primary α-Al phase caused by AC magnetic field, therefore, the change of thermoelectric potential difference could be used to characterize the effect of AC magnetic field on the microstructure of the alloy melt of Al-0.99%Fe hypoeutectic alloy.

Fund: Supported by China Postdoctoral Science Foundation Funded Project (No.2015M571320) and Fundamental Research Funds for the Central Universities (No.N150504002)

Jianfeng ZHANG, Qing LAN, Qichi LE. Investigation on the Change of Thermoelectric Power of Al-Fe Hypoeutectic Alloy Melt Caused by AC Magnetic Field. Acta Metall Sin, 2018, 54(7): 1042-1050.

Fig.1 Schematic of the experiment equipment (1—alternating current (AC) power; 2—heating and protection system; 3—excitation coil; 4—sample container; 5—temperature measuring device; 6—data acquisition; 7—dual time relay; 8—resistivity measurement)

Fig.2 Effect of AC magnetic field on the thermoelectric potential difference between two electrodes of Al-0.99%Fe alloy melt (U—thermoelectric potential difference; t—time; ΔU_{0}—the maximum variation of U; ΔU_{1}—the variation of U during fast recovery process; ΔU_{2}—the variation of U during slow recovery process; ΔU_{3}—the residual variation of U; Δt_{0}—the magnetic field treating time; Δt_{1}—the fast recovery time; Δt_{2}—the slow recovery time; Δt—the total recovery time) (a) curve of U to t(b) curve of U, polyfit of U and its' first deriv-ative to t after stopping application of AC magnetic field

Fig.3 Curves of characteristic parameters of thermoelectric potential difference to temperatures (T)(a) curves of ΔU_{0} and ΔU_{1} to T (b) curve of ΔU_{2} to T (c) curve of ΔU_{3} to T (d) curves of Δt_{1}, Δt_{2} and Δt to T

Fig.4 Curves of characteristic parameters of thermoelectric potential difference to magnetic frequency (f )(a) curves of ΔU_{0} and ΔU_{1} to f (b) curve of ΔU_{2} to f (c) curve of ΔU_{3} to f (d) curves of Δt_{1},Δt_{2} and Δt to f

Fig.5 Curves of characteristic parameters of thermoelectric potential difference to exciting current (I)(a) curves of ΔU_{0} and ΔU_{1} to I (b) curve of ΔU_{2} to I (c) curve of ΔU_{3} to I (d) curves of Δt_{1}, Δt_{2} and Δt to I

Fig.6 Curves of characteristic parameters of thermoelectric potential difference to loading time (Δt_{0}) (a) curves of ΔU_{0} and ΔU_{1} to Δt_{0} (b) curve of ΔU_{2} to Δt_{0} (c) curve of ΔU_{3} to Δt_{0} (d) curves of Δt_{1}, Δt_{2} and Δt to Δt_{0}

Fig.7 Solidification microstructures of Al-0.99%Fe alloy quenched from 680 ℃ (a, b), 705 ℃ (c, d), 725 ℃ (e, f) and 765 ℃ (g, h) without (a, c, e, g) and with (b, d, f, h) AC magnetic field

Fig.8 Curves of ΔU_{3} of Al-0.99%Fe hypoeutectic alloy melt and the change of size of the primary α-Al phase (Δd) caused by AC magnetic field to temperatures

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