Mechanism of second-phase spheroidization driven by Fe/Si ratio and the associated mechanical response in as-cast 1060 aluminum alloy

The continuous rolling of 1060 commercial purity aluminum foils for lithium-ion batteries demands superior plastic deformation capacity, which is often severely impaired by coarse, brittle primary phases formed during solidification. To address this issue from the source, t he effect of the Fe/Si mass ratio (ranging from 1 to 4) on the microstructural evolution, phase selection, and mechanical properties of as-cast 1060 aluminum alloys is systematically investigated. Utilizing advanced microstructural characterizations and Scheil-Gulliver thermodynamic simulations, the results demonstrate that a low Fe/Si ratio of 1 predominantly yields coarse, Chinese-script α-AlFeSi phases with a high average aspect ratio of 2.25. Conversely, increasing the Fe/Si ratio to 4 triggers a significant spheroidization transition, transforming the precipitates into highly dispersed, spherical metastable Al m Fe phases with a reduced average aspect ratio of 1.95. Thermodynamic and kinetic analyses reveal that the high Fe/Si ratio creates a Si-depleted environment that suppresses the formation of Si-rich stable phases, while massive casting undercooling kinetically favors the rapid nucleation of the metastable Al m Fe clusters. From a micromechanical perspective, these spheroidized metastable phases alleviate localized stress concentrations, achieve uniform load dispersion, and delay the nucleation and coalescence of interfacial microvoids during deformation. Consequently, optimizing the Fe/Si ratio increases the fracture elongation of the alloy from 24.9% to 28.0%, providing a reference for the composition design and initial microstructure control of aluminum foil billets.