Effect of La/Ce co-addition on the microstructure and properties of recycled Al-Mg-Si alloys

This study systematically investigates the effects of low-cost rare earth elements La and Ce on tailoring the microstructure and properties of recycled Al-Mg-Si alloys, with particular emphasis on enhancing sustainability-oriented performance. Minor additions of La and Ce effectively refine the α-Al grains and transform their morphology from coarse dendritic structures to equiaxed grains, leading to a reduction in the average grain size from 430.1 μm to 195.9 μm under the combined addition condition. More importantly, the detrimental Fe-rich β-Al 5 FeSi phases are markedly modified from coarse needle-like morphologies into fine and uniformly distributed particles, accompanied by a decrease in both their size and area fraction. Thermodynamic analysis indicates that La and Ce facilitate the formation of rare-earth intermetallic compounds (e.g., AlFeLa, AlCeSi, AlLaSi, and Al(La,Ce)Si 2 ). These compounds simultaneously consume Fe and Si, thereby suppressing the formation of harmful Fe-rich phases while providing heterogeneous nucleation sites for α-Al. This combined influence of the solidification behavior results in simultaneous improvements in strength, ductility, and thermal conductivity. The alloy with combined La/Ce addition exhibits an ultimate tensile strength of 164.5 MPa, an elongation of 18.2%, and a thermal conductivity of 179.7 W·m -1 ·K -1 . These findings demonstrate an effective and economically viable strategy for enhancing recycled Al-Mg-Si alloys, providing substantial potential for the high-value utilization of aluminum scrap and contributing to the advancement of sustainable materials development.