RI-ITMT method was applied to improve the toughness of Al-Li system alloy. This method was found to be effective for the improvement of the toughness of Al-Li system alloy. The significantly finer grains were obtained by RIITMT method. However, the greatest toughness was not necessarily obtained in the finest grain size. The improvement in toughness was achieved in the specimens in which the second phase particles precipitated during overaging treatment in thermomechanical treatment process had remained after the final solid solution and aging treatment. Therefore, the improvement in toughness was achieved by preventing the stress concentration to the grain boundary, caused by the large planner slip, by the introduction of the second phase particles in addition to grain refinement. In addition to the Al3Zr precipitate, Cu-rich precipitate also formed duplex phase with δ’ precipitate. The heat treatment in Ar atmosphere was more effective in preventing the phenomenon of Li loss. However, it was impossible to prevent Li loss completely. Under the dynamic loading condition toughness increased due to the shear-lip associated with Li lost layer.
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