Nanoscale Fe-containing intermetallic formation in Al-Fe-Mn-Si alloys: Unveiling a rare explosive nucleation pathway under liquid confinement

Iron (Fe) is an unavoidable impurity in recycled aluminium (Al), where the formation of Fe-containing intermetallic compounds (Fe-IMCs) severely reduces ductility and performance due to their coarse morphology. The nucleation difficulty of Fe-IMCs remains a critical barrier to both Fe removal efficiency and refinement of Fe-IMCs as secondary phases, limiting the use of recycled feedstock in high-performance applications. Conventional approaches have focused on development potent grain refiners to promote heterogeneous nucleation by providing structural and compositional templating. However, despite advances in nucleation theory and refiner development, significant refinement of Fe-IMCs has proven elusive. In this study, we report an unexpected case of impeding heterogeneous nucleation, where nanoscale Fe-IMCs explosively form within confined oxide films in an Al-Fe-Mn-Si alloy. Using advanced scanning transmission electron microscopy (STEM) we reveal that dense amorphous oxide films and carbides act as substrates for impeding nucleation. These results highlight how that confinement oxide films can activate non-classical nucleation pathways, offering the other possibility to control Fe-IMC formation and enhance the upcycling potential of recycled Al alloys. • High density of nanoscale α-Al 15 (Fe,Mn) 3 Si 2 particles were solidified within confined oxide films in an Al-1Mn-2.2Fe-5Si alloy. • The oxides and inclusions within this confined oxide film are amorphous. • The Si phase, which is as difficult to nucleate as Fe-IMCs, was also refined to the nanoscale within this confined melt.