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 T-1) by solid-state precipitation. We found that a controlled, long time low-temperature ageing (LTA) at 85 degrees C was sufficient to continuously mediate the fine precipitation in between T-1 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 T-1 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 delta', theta'/GP zones and T-1 is available and in the meantime significant coarsening of delta' precipitates is unattainable.