Aircraft alloy
Duralumin - Al-Cu alloy - hardens over days at room-temperature after
being quenched from solution-treated (essentially annealed state) -
but as far as I know that then stays permanent. There isn't really
any driving-force even in geological time (for mountains to flow into
the sea (!)) for the structure to coarsen and loose yield strength.
As far as I know ???
Rich S
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