The evolution of precipitates and mechanical properties in rapidly solidified 2195 Al-Cu-Li alloy during thermal exposure

The thermal stability of Al-Cu-Li alloy is critical to the quality and reliability of aerospace structural components. In this work, the microstructure and properties of rapidly solidified Al-Cu-Li alloy (T84) thermally exposed at 150 degrees C, 175 degrees C, 200 degrees C and 225 degrees C for 500 h were systematically studied. The results show that the T84 alloy exhibits excellent thermal stability with increased strength after thermally exposed at 150 degrees C, which is attributed to the increased number density of the T1 phase -Al2CuLi. With the further increase of thermal exposure temperature, the size of the T1 phase increases, the number density decreases significantly, and coarse precipitates such as T2 phase-Al6CuLi3 are formed. Meanwhile, the grain boundary precipitates coarsen and the precipitation free zones widen. The strengthening mechanism of the T1 phase transforms from shear mechanism to by-passing mechanism, and its contribution to yield strength decreases dramatically. In addition, the calculated activation energy indicates that coarsening of the T1 phase is controlled by the diffusion of Cu atoms.