Studies on activation energy of superplastic dynamically recrystallized aluminum-lithium alloys

When dispersiods are added to single phase alloys, the grain growth during recrystallization is inhibited. In certain alloys, this can lead to superplasticity. Fine grains are obtained prior to the superplastic deformation and subsequent grain growth is inhibited by the dispersoids, a process called "dynamic recrystallization". One such alloy group that can be processed using this technique is Al-Li. This study was designed to determine the activation energy associated with dynamic recrystallization in three alloys: 2090-OE16-Al-2.2Li-2.7Cu- 0.12Zr; 8090-Al-2.5Li-2.7Mg-0.12Zr; and Weldalite-Al-1.3Li-4.75Cu-0.4Ag-0.4Mg-0.14Zr- 0.03Ti. All tests were conducted with sheet specimens 0.0024 m thick with 0.0064 m gage length. The activation energies were derived from constant true strain rate tests at a variety of temperatures. The data and examination of microstructures show that the microstructural behavior of dynamically recrystallized Al-Li is characteristically different from statically recrystallized superplastic pseudo single phase alloys. Both dislocation network and grain boundary sliding play significant roles in the superplastic deformation. This is reflected in the changes in the activation energy.