Growth twins within (Al₃(Sc,Ti) + α-Al) eutectic cells enable novel grain refinement in recycled Al alloys

Abstract

Designing sustainable aluminium alloys with superior mechanical performance requires effective microstructural control during solidification. In this study, a cross-over recycled wrought aluminium alloy system spanning the 1xxx–7xxx series was designed with maximum impurity tolerance. A grain refinement strategy using hypoeutectic Sc additions was developed to simultaneously refine grains and second-phase particles. A previously unreported grain refinement mechanism was identified in this multicomponent recycled alloy, where the growth of α-Al grains is constrained by a network of (Al + Al3(Sc,Ti)) eutectic cells rather than by classical heterogeneous nucleation. Remarkably, α-Al growth twins were observed within these eutectic cells, a crystallographic feature rarely reported in high stacking-fault-energy aluminium. Atomic-scale characterization using scanning transmission electron microscopy (STEM) reveals the structural characteristics associated with this phenomenon. These findings provide a new pathway for microstructural control in complex recycled aluminium alloys and offer design principles for next-generation sustainable lightweight materials with enhanced mechanical performance.