Enhanced strength and ductility in an Al–Cu–Li alloy via long-term ageing

High-strength Al–Cu–Li alloys are increasingly attractive for aerospace applications. The highest-strength Al–Cu–Li alloys require a series of high-temperature ageing coupled with strain imposed before or during ageing to form a high number density of precipitates (particularly T1) by solid-state precipitation. We found that a controlled, long time low-temperature ageing (LTA) at 85 °C was sufficient to continuously mediate the fine precipitation in between T1 platelets in a 2195 Al–Cu–Li alloy following T8 treatment. The microstructures caused by LTA were more uniform than those characteristic of T8 condition, along with the reduction of precipitate-free zones (PFZs) between T1 platelets, which resulted in better material strength and elongation properties. The LTA method is supposed to be particularly useful in Al–Cu–Li alloys with low Li and high Cu contents, in which complementary precipitation of a fine mixture of δ′, θ′/GP zones and T1 is available and in the meantime significant coarsening of δ′ precipitates is unattainable.