For a metal such as aluminium, quenched to give a high concentration of retained vacancies, the annealing process takes place in two stages, as shown in Figure 4.8; stage I near room temperature with an activation energy ???0.58 eV and n ??? 104 , and stage II in the range 140???200??? C with an activation energy of ???1.3 eV. Assuming a random walk process, single vacancies p would migrate an ave