Experimental investigation and numerical study on evolution of surface roughness caused by ultrasonic shot peening of 2024 aluminum alloy sheet

Ultrasonic shot peening (USP) is widely used for materials surface strengthening and metal sheet forming as a novel mechanical surface treatment technology. The USP-caused surface roughness is usually viewed as an unfavorable factor influencing the service performance of the mechanical components treated by USP. Taking advantages of the experimental investigation, analytical calculation and finite element simulation, the correlation between the USP-caused surface roughness and the USP-induced metal sheet forming deformation is studied comprehensively. Firstly, the USP intensity was experimentally tested by USP of Almen strips. In accordance with the USP intensity, the experimental investigations on the evolutions of surface roughness caused by USP of 2024 aluminum alloy sheets with the thicknesses of 1 mm, 2 mm and 3 mm were carried out, respectively. An analytical calculation model (ACM) was then proposed to account for the effects of the USP-induced metal sheet forming deformation on the USP-caused surface roughness. The analytically-calculated results are in good agreement with the experimentally-measured surface roughness caused by USP of 2024 aluminum alloy sheets. Lastly, linking the finite element simulation of the USP-induced metal sheet forming with the analytical calculation model, an innovative FEM-ACM coupling approach was presented for predicting the evolutions of surface roughness caused by USP of metal sheets. It has been experimentally validated with USP of 2024 aluminum alloy sheets, and would be of great significance for the development and industrial application of USP technology.