Thermal stability of Al3(Scx,Zr1−x)-dispersoids in extruded aluminium alloys

In aluminium alloys the highest resistance against recrystallisation is obtained through combined additions of Sc and Zr. Upon annealing these elements form a high number density of homogeneously distributed and coherent Al3(ScxZr1−x)-L12-dispersoids, and the coarsening of these phases subsequently control the softening processes of recovery and recrystallisation. In this work the kinetics of Al3(ScxZr1−x)-coarsening has been investigated during annealing of two precipitation annealed and extruded Al–(Mn)–Fe–Si–Sc–Zr-alloys at temperatures between 500 °C and 600 °C. A simple analysis based on widely used theories for volume diffusion controlled dispersoid coarsening (R3(t) − R03 ∝ t) was used to identify the dominant mechanisms. It was found that coarsening in both alloys is controlled by volume diffusion of Zr, as activation energies, Q, of 285 ± 31 kJ/mol and 250 ± 43 kJ/mol were obtained, respectively.