Kinetics of precipitation in Al-1 wt% Mn alloy

Precipitation kinetics in high purity Al-10 wt% Mn alloy has been investigated during the early stages of isothermal annealing between 823 and 698 K by resistivity measurements. Aged specimens were also examined by transmission electron microscopy. The precipitation kinetics can be represented by an Avrami type equation with the time exponentn=2/3 during the early stages of annealing. This can be attributed to the nucleation and growth of fiat needle-like precipitates on dislocations. The precipitates were Al₆ Mn at 773 K and the metastable G₂ -phase at 773 K. After prolonged annealing times at 848 K, isometric plates of Al₆Mn were also observed and the value ofn was found to be 1.0. However, at 698 K after longer annealing times, isometric needles of Al₁₂Mn, G-phase were observed along with flat needles of G₂ precipitate. At 698 K, the value ofn tends to decrease with time from 0.67 to 0.59.