Microstructures and mechanical properties of Al-Li 2198-T8 alloys processed by two different severe plastic deformation methods: A comparative study

In this study, the microstructural evolution and mechanical properties of Al-Li 2198-T8 (artificially peak aged) separately processed by two typical severe plastic deformation (SPD) methods (i.e. friction stir processing (FSP) and high-pressure torsion (HPT)) were investigated. The microstructural examination showed that both FSP and HPT were capable of refining the grains for Al-Li 2198-T8, and the HPT processing produced much finer grains. Transmission electron microscopic observation revealed that precipitates of beta' (AlsZr), theta' (Al2Cu) and T1 (Al2CuLi) existing in the as-received Al-Li 2198-T8 fully dissolved after HPT, whereas the precipitates of beta' (Al3Zr) were retained in the processed zone after FSP. The hardness and tensile testing demonstrated that the hardness and strength of FSP-processed alloy significantly declined compared to the as-received alloy, while those of HPT-processed alloy substantially increased due to exceptional grain refinement and high dislocation density. The strengthening mechanisms of the alloy before and after the SPD processing were discussed in the present paper.