J. Mater. Sci. Technol. ›› 2019, Vol. 35 ›› Issue (7): 1422-1431.DOI: 10.1016/j.jmst.2019.02.002
• Orginal Article • Previous Articles Next Articles
Xuan Liu, Jilai Xue*(), Zhichao Guo, Cheng Zhang
Received:
2018-04-28
Revised:
2018-10-12
Accepted:
2018-12-22
Online:
2019-07-20
Published:
2019-06-20
Contact:
Xue Jilai
About author:
1These authors contributed equally to this work.
Xuan Liu, Jilai Xue, Zhichao Guo, Cheng Zhang. Segregation behaviors of Sc and unique primary Al3Sc in Al-Sc alloys prepared by molten salt electrolysis[J]. J. Mater. Sci. Technol., 2019, 35(7): 1422-1431.
Fig. 2. Voltammogram of electrolysis process with carbon anode and liquid Al cathode in electrolyte of Na3AlF6-19%KF-29%AlF3-2%CaF2, 2 wt% Sc2O3, and T = 1073 K.
No. | Temp, T (K) | Time, t (h) | Current density, I, (A·cm-2) | Sc2O3 addition, A (wt%) | Cooling rate, C (K·s-1) | Sc (wt%) |
---|---|---|---|---|---|---|
1 | 1023 | 0.5 | 1 | 2 | 30 | 0.23 |
2 | 1023 | 1 | 1 | 2 | 0.43 | |
3 | 1073 | 1 | 1 | 2 | 0.66 | |
4 | 1073 | 1 | 1 | 4 | 0.93 | |
5 | 1073 | 2 | 1 | 4 | 0.75 | |
6 | 1073 | 1 | 2 | 4 | 1.38 | |
7 | 1073 | 2 | 1 | 4 | 0.5 | 0.67 |
8 | 1073 | 2 | 1 | 4 | 100 | 0.59 |
Table 1 Sc contents of the electrolytic Al-Sc alloys under different conditions.
No. | Temp, T (K) | Time, t (h) | Current density, I, (A·cm-2) | Sc2O3 addition, A (wt%) | Cooling rate, C (K·s-1) | Sc (wt%) |
---|---|---|---|---|---|---|
1 | 1023 | 0.5 | 1 | 2 | 30 | 0.23 |
2 | 1023 | 1 | 1 | 2 | 0.43 | |
3 | 1073 | 1 | 1 | 2 | 0.66 | |
4 | 1073 | 1 | 1 | 4 | 0.93 | |
5 | 1073 | 2 | 1 | 4 | 0.75 | |
6 | 1073 | 1 | 2 | 4 | 1.38 | |
7 | 1073 | 2 | 1 | 4 | 0.5 | 0.67 |
8 | 1073 | 2 | 1 | 4 | 100 | 0.59 |
Fig. 3. Photographs and XRD spectra of prepared Al-Sc alloys. (a) Section view of the alloy in a electrolysis cell; (b) Alloy product (T = 1073 K, I = 1 A/cm-2 and t = 1 h. Cooling rate, C = 30 K/s); (c) and (e) XRD patterns of Al-0.23 wt%Sc and Al-0.93 wt% Sc alloys, respectively. (d) and (f) Optical micrographs corresponding to (c) and (e), respectively.
Fig. 5. The optical micrographs taken from different locations in the Al-Sc alloys prepared by electrolysis. (T = 1073 K, I = 1 A/cm2, t = 2 h, C = 30 K·s-1, and Sc = 0.75 wt%). (a) The schematic of Sc content of Al-Sc alloys at different positions by ICP-AES analysis; (b)-(g) Micrographs of Al-Sc alloys corresponding to (a), respectively.
Fig. 6. Optical micrographs of the prepared Al-Sc alloys at different cooling rates. (a) Schematic for observation positions; (b) and (c) 0.5 K/s (side and bottom position, respectively); (d) 100 K/s (right top side position); (e) Magnified picture of (c).
Fig. 7. Hypothetical schematics for Sc segregation in Al-Sc alloy prepared by electrolysis. (a) A schematic for the interface of Al-Sc alloys and molten salts during electrolysis; (b) A hypothetical diagram of Sc distributing layer around the edge of Al-Sc alloy (T = 1073 K, I = 1 A/cm2, t = 1 h, C = 30 K·s-1, and Sc = 0.93 wt%).
Fig. 8. Distribution of primary Al3Sc in the prepared Al-Sc alloy (T = 1073 K, I = 2 A/cm2, t = 1 h, C = 30 K/s, and Sc = 1.38 wt%). (a) Schematic for observation positions; (b) at top location; (c) at right location; (d) at bottom location; (e) at right-down location. (f) Corresponding area fraction of primary Al3Sc phase at different locations; (g) Schematic for the electric charge density distribution.
Fig. 9. Morphologies of primary Al3Sc in this work and schematic drawings for the two-dimensional planes (T = 1073 K, I = 2 A/cm2, t = 1 h, C = 30 K/s, and Sc = 1.38 wt%).
Fig. 10. SEM images of the unique primary Al3Sc phase in Al-Sc alloys. (a) Morphology of dendritic primary Al3Sc in Al-0.75 wt%Sc alloy (I = 1 A/cm2, C = 30 K/s, t = 2 h, 1 mm from the left downside edge); (b) SEM mapping of the primary Al3Sc in Fig. 10a; (c) the dendritic Al3Sc in the Al-0.67 wt%Sc alloy (I = 1 A/cm2, C = 0.5 K/s, t = 2 h, bottom position); (d) the faceted cuboid Al3Sc in Al-0.67 wt%Sc alloy (I = 1 A/cm2, C = 0.5 K/s, t = 2 h, top position).
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