Structural evolution and grain growth kinetics during isothermal heat treatment of nanostructured Al6061

Grain growth kinetics of nanostructured Al6061 powder prepared via mechanical milling was studied through isothermal heat treatment. The results showed that after 30 h of milling, the powder was composed of an Al-based supersaturated solid solution with a grain size of 35 nm and lattice strain of 0.43%. Release of lattice strain, intermetallic precipitation and grain growth occurred upon heating of the 30 h-milled powder. Nevertheless, grain growth was very limited and Al grains with size of 50–60 nm were still present after exposure to 550 °C (0.83Tm) for 3 h. The activation energies for the grain growth were found to be 112.3 kJ/mol for annealing at 150–300 °C and 148.4 kJ/mol for annealing at 350–550 °C. Additionally, the isothermal grain growth exponent (n) was obtained in the range of 0.024–0.21.