Solute repositioning to tune the multiple microalloying effects in an Al–Cu alloy with minor Sc, Fe and Si addition

For multicomponent Al-based alloys, one of the most valuable approaches of microstructural design is to find a path to maximize the multiple microalloying effects while overcoming their negative counterparts. In this paper, triple Sc-Fe-Si microalloying was performed in an Al–Cu alloy to assemble the co-existence of θ′-Al₂Cu and Al₃Sc precipitates. Besides, the mutual interactions among triple microalloying elements were utilized to maximize the positive effects on tailoring the dual precipitates, as illustrated in two goals of microstructural design: (i). As to θ′-Al₂Cu plates, the multiple Sc-Fe-Si segregation at θ′-Al₂Cu/matrix interface was preferentially created in the alloy before creep (as-aged condition). During subsequent high-temperature creep, such interfacial warden will be rapidly reinforced by solute repositioning, as a process of accumulating solutes diffusing from both inner θ′-Al₂Cu precipitate and outer matrix to limit the interfacial migration. (ii). For Al₃Sc precipitates, the beneficial Si microalloying effect on encouraging the nucleation of Sc-rich entities (precursor of Al₃Sc) was successfully acquired during aging, while the detrimental Si effect on accelerating Al₃Sc coarsening is generally prohibited by tuning Fe–Si synergy within Al₃Sc interior. The establishments of (i) and (ii) enable the satisfactory dispersion as well as the outstanding thermal stability of dual precipitates in the current Al-Cu-Sc-Fe-Si system, leading to a good creep resistance at a high homologous temperature of 0.61T_m ~ 300 °C (where T_m is the melting temperature of the α-Al matrix).