Improving mechanical properties and thermal stability of Al-Si-Mg alloy via synergistic Cd and Cu microalloying

This study reports a cast Al-Si-Mg alloy exhibiting significantly enhanced age-hardening response via Cd and Cu additions. Strong Cd-Mg-vacancy, Cd-Si-vacancy and Cd-Cu-vacancy binding promote rapid formation of Cd-Mg-Si(-Cu) clusters, accelerating initial age-hardening kinetics. These clusters evolve into abundant composite structures of Cd-rich precipitates epitaxially connected with β″/Q′/C precipitates, elevating peak-aged strength. Additionally, over-ageing softening is suppressed via (i) Cd-refined precipitate size and homogenized size distribution, and (ii) slow-coarsening Cu-containing Q′/C precipitates. The resulting high density of fine precipitates promotes strong work hardening, conferring superior ductility under both peak- and over-aged conditions.