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

The microstructure evolution and strengthening mechanism of materials after shot peening have always been the focus of research. In this paper, a novel coupled constitutive model was proposed to predict the depth of fine-grain of the 2060-T8 aluminum-lithium (Al–Li) alloy after shot peening. Besides, combining the numerical and experimental methods, the influences of shot size on yield stress, dislocation density, and crystal orientation of Al–Li alloy were systematically studied to reveal the strengthening mechanism. The results show that larger shot sizes can significantly improve the depth of the dislocation density layer and the fine-grain layer of 2060 Al–Li alloy. The depth of the refinement layer increases from 50 μm to 80 μm when the shot size grows from 0.3 mm to 0.6 mm. It is found the depth of the grain refinement layer in the experiment is consistent with the depth where is a sudden change of grain size in the simulation. Additionally, electron backscatter diffraction (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%. The crystal orientation in the grain has changed obviously and Goss texture {100} obtained in the deformation band. In contrast, with the increase in shot size, the proportion of the Schmid factor with a high-level trend increases. However, the hardening effect of the material is much greater than the softening effect which results in higher yield stress and microhardness of the top surface.