Room temperature instability of an Al-4%Cu super saturated solid solution in a nano-crystalline alloy produced by SPD

The long-term stability of a severely deformed aluminium alloy has been investigated when copper in solution is used to inhibit recovery. A grain thickness of only 70 nm was obtained in an Al-4 wt% Cu alloy, after processing by equal channel angular extrusion to a strain of εeff ∼ 15, resulting in a lamellar nano-grain structure. However, the severely deformed solid solution was found to be unstable at room temperature and copious precipitation of θ occurred at new grain boundaries within the deformed state. The solute level fell to equilibrium within ∼9 months. The precipitation kinetics were shown to occur at many orders of magnitude higher than can predicted by classical theory. © 2010 Springer Science+Business Media, LLC.