Effects of ultrasonic treatment on microstructure and mechanical properties of recycled Al-9Si-1Fe alloy

To solve global resource and environmental challenges, it is very important to replace electrolytic aluminum alloys using recycled aluminum alloys. However, Fe as an impurity element is inevitably introduced into aluminum alloys during the recycling process, which deteriorates the mechanical properties of the alloys, particularly ductility. Therefore, this study investigates the influence of ultrasonic treatment (UT) on the microstructure and mechanical properties of the Al-9Si-1Fe alloy, focusing on the refinement and strengthening mechanisms of the alloy under different ultrasonic power treatments. Ultrasonic power levels of 0 W, 500 W, 1000 W, 1500 W, and 2000 W were applied to the alloy, and the results indicate that ultrasonic treatment significantly refines the microstructure. The best refinement effect is achieved when 2000 W ultrasonic power is used to treat the Al-9Si-1Fe alloy melt, the α-Al phase is transformed from large dendrites to small equiaxed crystals. Also, the eutectic Si was modified from coarse needle to short rod, the Fe-rich (β-Al₅FeSi) phase was significantly refined from long slate-like to short rod. Meanwhile, the α-Al₄Fe₂Si phase precipitated in the form of tiny Chinese script during solidification. Room temperature tensile tests showed that the UTS of the Al-9Si-1Fe alloy increased from 148 MPa to 188 MPa after ultrasonic treatment at 2000 W. Additionally, elevated temperature tests indicated that the UTS increased from 141 MPa to 165 MPa at 200 °C. Moreover, the elongation (EI) was increased from 1.26 to 1.90% at room temperature and from 2.08 to 2.88% at 200°C.