Surface gradient microstructural characteristics and evolution mechanism of 2195 aluminum lithium alloy induced by laser shock peening

The peak-aged 2195 aluminum lithium alloy was treated by laser shock peening (LSP). The surface gradient microstructural characteristics of this alloy induced by ultrahigh strain rate deformation during LSP were systemically examined with transmission electron microscope (TEM), the observed results suggested that the grains refined and precipitates partially dissolved in the surface after LSP. The original coarse grains with average size of about 16 μm in length and 5 μm in width were refined instantly to equiaxed grains with size of about 91 nm at the top surface after LSP. The quantitative calculation of recrystallization kinetics proved that the grain refinement was the result of rotation dynamic recrystallization (RDR). The adiabatic temperature increase, the generation of high-density dislocations around the precipitates, and the increase of grain boundary area caused by grain refinement provided the thermodynamics and kinetics conditions for partial dissolution of precipitates. The microhardness tested results showed gradient distribution characteristics of microhardness values after LSP, and the maximum of microhardness was at the top surface of this alloy. The refined grains and deformed substructures played important roles on the enhancement of surface microhardness.