Surface layer strengthening mechanism of 2060 aluminum–lithium alloy after shot-peening

The strengthening mechanism of the 2060-T8 aluminum-lithium (Al-Li) alloy after shot peening was revealed through the numerical and experimental methods in this paper. Based on the modified coupled constitutive model describing the reinforcement resulting from grain refinement was applied, the influences of shot size on residual stress, dislocation density, crystal orientation and grain refinement of Al-Li alloy were systematically studied with random shot finite element analysis. The results show that larger shot sizes can significantly improve the depth of the dislocation density layer and fine grain layer of 2060 Al-Li alloy. The depth of the refinement layer increases from 50μm to 80μm when the shot size increases from 0.3mm to 0.6mm. The simulation results show high consistency with electron backscatter diffraction (EBSD) experiments. Due to the randomness of the impact position, the dislocation density and grain sizes are not evenly distributed across the surface in the simulation. Additionally, EBSD shows that many sub-grains are produced in the material due to high dislocation density, and the proportion of low-angle grain boundaries (LAGB) increases significantly, from 48.3% to more than 98.4%. With the increase of depth, obvious stratification of the plastic deformation region, transition region, and un-deformed region is demonstrated in the inner structure, which also indicates the gradient hardness of the material. Additionally, the crystal orientation in the grain has changed obviously and Goss texture{100}<001> obtained in the deformation band. Compared with small shots, larger shots can significantly influence the crystal orientation and improve the hardness of the materials under the same shot peening pressure and flow rate.