Selective silicon removal from AlSi scraps by Mg-assisted electromagnetic fractional crystallization

In the context of the transition toward vehicle electrification and lightweighting, end-of-life Al Si casting scrap is increasingly at risk of becoming “dead metal” because its high Si content prevents direct reuse in high-value aluminum products. In this study, an integrated Mg-assisted electromagnetic fractional crystallization route was developed to upcycle Al Si scrap. Thermochemical calculations demonstrated that Mg addition modifies the solidification path by converting eutectic Si into separable primary Mg 2 Si. Experiments using an Al-6.45%Si-28.54%Mg alloy showed that the Si content in the purified region decreased to 0.406 wt% under natural cooling, achieving a Si removal efficiency of 93.71%, which is close to the thermochemical prediction. However, the purified region area fraction was only 17.8%. The application of the electromagnetic field following the initial Mg 2 Si formation exhibited a negligible effect on the purified-region yield. In contrast, the application of a continuous alternating electromagnetic field during primary Mg 2 Si precipitation resulted in a significant enhancement of phase separation. As the coil current increased from 330 to 430 and 530 A, the central purified-region area fraction increased from 71.15% to 78.30% and 79.50%, while maintaining a high Si removal efficiency of 93.36–93.76%. The separation mechanism is attributed to the Mg-induced phase transformation, Lorentz force-driven convection, electromagnetic-assisted Mg 2 Si migration, and preferential growth near the colder crucible wall. The resulting low-Si Al Mg alloy could subsequently be treated by vacuum distillation to remove Mg, while the recovered Mg could be recycled in the upstream crystallization process. The present study proposes a promising and potentially scalable circular-economy route for upcycling Al Si casting scrap into high-value aluminum alloy products.