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 theta'-Al2Cu/matrix interfaces were investigated in an Al-Cu-Sc alloy crept at beyond 300 degrees 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 theta'-Al2Cu were demonstrated: (1) The Al3Sc precipitation was processed at the expense of the adjacent Sc segregation and allows localized theta'-Al2Cu decomposition, causing precipitate splitting. (2) The Al3Sc-enclosed growth ledges resultantly prevented theta'-Al2Cu from coarsening and equilibrium transformation to theta-phase at temperature as high as 400 degrees 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. (C) 2020 Elsevier B.V. All rights reserved.