Abstract: With the development of surface self-nanocrystallization technology of metallic materials, the metallic surface pro-perties have been enhanced to a certain degree. In this paper, the mechanism of surface nanocrystallization on 7A52 aluminum alloy after high-energy shot peening treatment (HESP) was characterized by SEM, EBSD,TEM and HRTEM. The results show that the microhardness increase with the increase of shot peening time. After 50 min HESP, the surface hardness is about 270HV, which can approximately increase to 1.5 times compared to the base metal; the average grain size is about 14.16 nm; the subsurface layer of 60 μm deep is composed of micrometers sub-grains. The surface layer grain refinement process of 7A52 aluminum alloy involves formation of dislocation pile-up and tangling, which resulted in deformed grains. Finally, nano-scale grains with equiaxed shape and random crystallographic orientations are formed upon the multidirectional repeated loads.
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