Nucleation and growth of Al3Sc precipitates during isothermal aging of Al-0.55 wt% Sc alloy

Abstract

The nucleation and growth process of Al 3 Sc precipitates in Al-0.55 wt% Sc alloy during isothermal aging was studied by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). It is found at the early aging stage that the solute Sc atoms are enriched on the stacking fault in the matrix then rapidly converted to L1 2 -ordered Al 3 Sc precipitates without the formation of other transition phases. The matrix and precipitates form a sharp interface at the beginning of phase transition and maintain a completely coherent crystallographic orientation relationship. Due to the influence of the anisotropy of interface energy, the equilibrium shape of the precipitated phase is similar to the spherical polyhedron. In the coarsening stage of precipitates, the interface of α-Al/Al 3 Sc gradually changes from coherent to semi-coherent, resulting in the gradual loss of symmetry of the non-contrast line, and finally the stress field contrast on the surface of particles and interface dislocations gradually appear. • The solute Sc atoms are enriched on the SF in the matrix. • The precipitate sequence of Al-0.55wt.%Sc alloy at 523K is SSSS → Solute clusters → Al 3 Sc.