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 Al-3(ScxZr1-x)-L1(2)-dispersoids, and the coarsening of these phases subsequently control the softening processes of recovery and recrystallisation. In this work the kinetics of Al-3(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 degrees C and 600 degrees C. A simple analysis based on widely used theories for volume diffusion controlled dispersoid coarsening (R-3(t)-R-0(3) alpha 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/moI were obtained, respectively. (c) 2007 Elsevier B.V. All rights reserved.