Long-term thermal ageing of the 2219-T851 and the 2050-T84 Al-Cu alloys

In this study, the influence of high temperature exposure on mechanical properties as well as on the microstructures of two Al-Cu alloys, has been investigated. Driven by an industrial will to use structural aluminium at higher temperature than usually stated, this work is focused on the characterization of the evolution of two commercial alloys, the 2219-T851 and the 2050-T84, induced by an ageing treatment of 1000 h at 200 degrees C. Careful TEM observations confirm the importance of the nanoscale precipitation and that the precipitate size and distribution strongly influence the mechanical properties of the studied alloys. Results unexpectedly show that the theta ' -Al2Cu precipitates are more stable in time than the T1 -Al2CuLi precipitates at this temperature. Regarding the mechanical properties related to ageing, it follows that the 2219-T851 alloy presents a reduced drop with time of its tensile test curves compared to the 2050-T84, thus a limited, and at least less pronounced, temperature dependence. For an industrial application on structural part, 2219-T851 alloy then appears to be a good candidate for long-term structural applications at intermediate temperatures.