Solid-State Reactive Processing of Al–Fe ₃ O ₄ Nanothermites for In Situ Formation of Soft-Magnetic Fe Nanoparticles in an Aluminum Matrix

We present a solid-state reactive processing (SSRP) route that enables in situ formation and uniform dispersion of metallic Fe nanoparticles within an aluminum matrix through controlled nanothermitic reactions. Using friction-assisted plastic deformation of an Al–Mg alloy embedded with a small fraction (∼4 wt %) of Fe3O4 particles, localized heat and shear deformation promote concurrent mechanical mixing, thermal activation, and chemical reduction. The reaction between Fe3O4 and Al/Mg produces Fe cores encapsulated by MgO and Al2O3-rich shells, effectively suppressing the formation of brittle Fe–Al intermetallics that typically hinder Fe-reinforced Al systems. The resulting microstructure exhibits fine-scale dispersion of core–shell nanoparticles and significant matrix refinement, leading to enhanced hardness and electrical resistivity. This proof-of-concept demonstrates that multistimuli coupling during solid-state processing can activate in situ controlled thermite reactions at moderate temperatures, providing a new pathway for fabricating lightweight, multifunctional metal–oxide nanocomposites.