Abstract
The growth kinetics of δ′ (Al 3Li) precipitate free zones (PFZ) at the grain boundaries has been investigated in several Al-Li alloys at selected aging temperatures ranging from 168 to 225°C and aging times. The PFZs form by a solute depletion mechanism and the PFZ growth can be described as a diffusion controlled process. The activation energy for PFZ growth has been evaluated as 144 kj/mol, which agrees with the activation energy evaluated for the diffusion of Li in α-Al. The PFZ growth has been analyzed on the basis of a diffusion model with due consideration of δ (AlLi) formation at the grain boundaries. With increase in Li content in the alloys, the growth rate of PFZ increases. This observation is explained by a possible increase in the interdiffusion coefficient with the alloy composition. The effect of grain morphology on the PFZs has been studied by comparing the PFZs in recrystallized and unrecrystallized Al-Li alloys.
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