Coarsening of cuboidal Al3Sc precipitates in an Al–Mg–Sc alloy

Abstract

The coarsening of {001}-faceted cuboidal Al3Sc precipitates in an Al–Mg–Sc alloy during ageing at 698, 723 and 748 K have been examined by the transmission electron microscopy and the electrical resistivity. Application of the theory of Kuehmann and Voorhees for the coarsening of second-phase precipitates in ternary systems, generalised to any centro-symmetric precipitates, has enabled the independent derivation of the {001} interface energy without assuming the values of the diffusivity of solute atoms (Sc and Mg) in the Al matrix. The {001} interface energy is estimated as 0.19 J/m2, which is in excellent agreement with the value of 0.192 J/m2 obtained using the first-principles calculation method. The sphere-to-cuboidal shape change of the Al3Sc precipitate during ageing is discussed by means of a simple energy consideration.