Kinetics and mechanisms of precipitation in an Al-0.2Â wt.% Sc alloy

Specimens of an Al-0.2 wt.% Sc alloy were solution heat treated and isothermally annealed in the temperature range of 190-530 °C, and the precipitation reaction was followed with electrical conductivity measurements. Some specimens were also examined by using light microscopy and transmission electron microscopy. The conductivity measurements were used to characterise the kinetics of the transformation, and a TTT (time-temperature-transformation) diagram was constructed. Two transformation time minima are observed, one at about 310 °C, which is associated with continuous precipitation and the other at about 410 °C which is associated with discontinuous precipitation. Conductivity measurements from the coarsening stage were used for estimating the solvus line of the phase diagram and the interface energy between Al and Al3Sc. Good solvus estimates were achieved in the temperature range of 370-530 °C. The estimates of interface energy spread from approx. 20 to 300 mJ/m2.