Ultrasonic refining mechanism of ternary phase in Al–Sc based alloys prepared through molten salt electrolysis
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摘要: 研究采用超聲協同熔鹽電解法制備Al–Si–Sc和Al–Cu–Sc合金，采用光學顯微鏡、掃描電鏡和X射線衍射研究超聲對合金中三元含鈧強化相形貌與尺寸的影響，進而闡明超聲細化機制。研究結果表明，協同超聲促使三元AlSiSc相由粗大菱形管狀轉變為細小實心方棒狀，其尺寸由205減小到40 μm左右；超聲顯著細化三元AlCuSc相團簇尺寸，由約100減小至約30 μm；超聲協同細化機制主要是通過提高形核率細化初生Al3Sc相并促進其均勻分布，進而作為形核發育基底，最終實現三元含鈧相細化；同時超聲也可促進合金溶質均勻分布，避免粗大Al3Sc相析出；超聲細化三元含鈧相機制主要作用于電解后凝固階段。Abstract: Aluminum alloys are widely used in cutting-edge technologies and emerging strategic industries, namely aerospace, high-speed rail transportation, electric vehicles, advanced functional materials, new energy storage, and conversion devices. The processability as well as the mechanical properties of aluminum alloys can be improved via the addition of trace scandium. The ultrasonically assisted molten salt electrolysis is a promising, short technical route for large-scale preparation of low-cost, Al–Sc-based alloys characterized by uniform and fine strengthening phases. At present, it is still unclear if that is the case for the ultrasonic refining mechanism of the Sc-bearing ternary phase. This study aims at clarifying the ultrasonic refining mechanism on the strengthening phase containing scandium. Two Al–Sc based alloys were prepared using ultrasonically assisted molten salt electrolysis while the effect of ultrasound on the morphology and size of the Sc-bearing ternary phase was studied using optical microscope, scanning electron microscope, and X-ray diffraction meter. The results show that the synergetic ultrasound facilitates the transformation of the ternary AlSiSc phase from the coarse rhombic tubes (~205 μm) to the short rod (40 μm). The cluster size of ternary AlCuSc phase is also greatly reduced from ~100 μm to ~30 μm. The ultrasonic refining mechanism is mainly related to the increase of the nucleation rate of the primary Al3Sc particles which are greatly refined and dispersed in the alloy melt before the solidification stage. The refinement of the Sc-bearing ternary phase is considered to be caused by the fine and disperse Al3Sc particles serving as nuclei. Furthermore, ultrasound can also aid the uniform distribution of solute field and prevent the precipitation of coarse Al3Sc phase. The effect of ultrasonic refinement of the ternary rhenium-containing phase is mainly present at the solidification stage after electrolysis.
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圖 2 超聲協同熔鹽電解Al–Si–Sc合金X射線衍射圖譜
Figure 2. XRD patterns of the Al–Si–Sc alloy, prepared by ultrasound-assisted molten salt electrolysis
圖 3 熔鹽電解Al–Si–Sc合金微觀凝固組織。（a～c）常規電解合金；（d）超聲協同電解合金；（e）超聲協同電解–凝固合金
Figure 3. Optical micrographs of the Al–Si–Sc alloy, prepared by molten salt electrolysis: (a?c) MSE; (d) US-MSE; (e) US-MSE/US-SOL
圖 5 超聲協同熔鹽電解Al–Cu–Sc合金X射線衍射圖譜
Figure 5. XRD patterns of the Al–Cu–Sc alloy, prepared by ultrasound-assisted molten salt electrolysis
圖 6 熔鹽電解Al–Cu–Sc合金微觀組織。（a）常規電解合金金相照片；（b）常規電解合金掃描電鏡形貌（插圖為深腐蝕后AlCuSc相）；（c～d）圖6（b）中點A和B的能譜圖；（e～f）超聲協同電解–凝固合金金相照片（插圖為深腐蝕后AlCuSc相掃描電鏡形貌）
Figure 6. Microstructures of the Al–Cu–Sc alloys prepared by molten salt electrolysis: (a) MSE (OM); (b) MSE (SEM, inserted figure showing the AlCuSc after deep etching); (c–d) EDS analysis of point A and B, respectively in Fig.6(b); (e–f) US-MSE/US-SOL (OM, inserted SEM figure showing the AlCuSc after deep etching)
圖 7 超聲協同熔鹽電解Al–Cu–Sc合金中三元AlCuSc相掃描電鏡形貌。（a） Al3Sc核心；（b）點A能譜圖分析；（c） AlCuSc外殼；（d）點B能譜圖分析；（e）包覆Al3Sc的AlCuSc相；（f）點C能譜圖分析
Figure 7. SEM micrographs of the AlCuSc ternary phase in Al–Cu–Sc alloy, prepared by ultrasound-assisted molten salt electrolysis: (a) Al3Sc nuclei; (b) EDS analysis of point A; (c) AlCuSc shell; (d) EDS analysis of point B; (e) Al3Sc covered by AlCuSc phase; (f) EDS analysis of point A
圖 8 熔鹽電解二元Al–Sc合金初生Al3Sc相形貌。（a）常規電解合金；（b）超聲協同電解合金；（c～d）超聲協同電解–凝固合金
Figure 8. Morphologies of the primary Al3Sc phase in the binary Al–Sc alloy, prepared by molten salt electrolysis: (a) MSE; (b) US-MSE; (c–d) US-MSE/US-SOL
圖 9 熔鹽電解含Sc鋁合金三元相超聲協同細化機制示意圖
Figure 9. Schematic for the ultrasonic refining mechanism of the ternary phase in the Al–Sc based alloys by molten salt electrolysis
中文字幕在线观看表 1 合金含鈧相尺寸量化結果
Table 1. Particle size of the Sc-containing phase in the investigated alloys
Alloy Particle size /μm MSE US-MSE US-MSE/US-SOL Al–Sc 96±34 48±12 22±7 Al–Si–Sc 205±82 228±96 40±10 Al–Cu–Sc 94±36 — 30±5 
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