Microstructural characterization of recycled Al–Mg–Si-based alloys upon the synergistic effect of ultrasonic technology (UT) and novel refiners

Ultrasound, as an efficient, clean, and safe processing technology, is widely used in industries. Grain refiners are widely used in the refinement of cast alloys. In this study, ultrasonic technology (UT) and Al-5Ti-1B refiner prepared by continuous rheological extrusion (CRE Al-5Ti-1B) were used to modify the recycled Al-Mg-Si-based alloy, and the microstructure and mechanical properties of the recycled Al-Mg-Si-based alloy were studied. The differences in porosity and grain refinement caused by ultrasonic power were discussed. Results showed that, increasing the ultrasonic power can effectively reduce the porosity of the recycled Al-Mg-Si-based alloy. The synergistic effect of UT and CRE Al-5Ti-1B refiner significantly refined α-Al grains and second phases. The increase of ultrasonic power can effectively cause deagglomeration while reducing the nucleation undercooling of α-Al, which promotes the refinement of the recycled Al-Mg-Si-based alloy and significantly improves the mechanical properties. The yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the recycled Al-Mg-Si-based alloy were 106 MPa, 210 MPa and 9.4%, respectively. When 0.2 wt.% CRE Al-5Ti-1B refiner was added and the ultrasonic power was 150W, the YS, UTS, and EL were improved by 12.8%, 28.8% and 228.4%, respectively.