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.　Copyright　©2019　Chinese　Journal　of　Engineering.　All　rights　reserved.