Effects of wet shot peening on microstructures and mechanical properties of a 2060-T8 aluminum-lithium alloy

In this work, wet shot peening (WSP) was investigated to modify the microstructures and mechanical properties of a 2060-T8 aluminum-lithium (Al–Li) alloy through numerical and experimental methods. Gradient distributions of plastic strain and strain rate induced by WSP were obtained from simulation via coupled Eulerian-Lagrangian method and fitted by exponential functions. They were the primary extrinsic factors determining microstructural evolution and deformation mechanisms. In parallel, the hardening behaviors and heterogeneous microstructures in the modified layer with a thickness of about 200 μm were characterized by experiments. Experimental results showed that WSP improved yield strength, tensile strength and the microhardness at surface respectively by 16.15%, 11.83% and 10%, but the total elongation was reduced by 30.18%. The significant improvement of strength was associated with the combined influences of nanocrystalline, severe lattice distortion, precipitates variation, dense dislocations and stacking faults. Moreover, the gradient hierarchical microstructures fabricated by the non-uniform deformation of WSP can promote the accumulation of geometrically necessary dislocations (GNDs). The corresponding back stress caused by GNDs would produce extra hardening effects. Consequently, a modified composite model considering various microstructures, the volume fractions of modified layers as well as material continuity was proposed to predict the mechanical properties of materials processed by surface treatments. The estimated yield strength was found to agree well with experimental results.