Si-mediated reassembly of interfacially segregated Sc atoms in an Al–Cu–Sc alloy exposed to high-temperature creep

The formation of second-phase particles by solid-state precipitation is well-known as the most effective strengthening method for the light-weight aluminum (Al) alloys. Here, the interfacial evolutions from Sc solute segregation to Al₃Sc precipitation at θ′-Al₂Cu/matrix interfaces were investigated in an Al–Cu–Sc alloy crept at beyond 300 °C. By considering the trace Si impurity, it is proposed that Al₃Sc precipitation preferentially occurs at the Si-concentrated interfacial locations, i.e. growth ledges. Two effects of interfacial Al₃Sc precipitation on θ′-Al₂Cu were demonstrated: (1) The Al₃Sc precipitation was processed at the expense of the adjacent Sc segregation and allows localized θ′-Al₂Cu decomposition, causing “precipitate splitting”. (2) The Al₃Sc-enclosed growth ledges resultantly prevented θ′-Al₂Cu from coarsening and equilibrium transformation to θ-phase at temperature as high as 400 °C. This work is expected to provide a precipitate-stabilizing strategy by interfacial architecture to maintain the closely spaced dispersion of precipitates and its strengthening contribution at elevated temperature.