An over peening effect of Al7050 mid-thick plates with continued multiple laser shock peening at the same positions

Abstract:

In this paper, an over peening effect was presented based on the researches of surface integrity and internal spall of Al7050 mid-thick plates with continued multiple laser shock peening (LSP) at the same positions. The dimensions of the samples were 50 mm × 50 mm × 5 mm (Length × Width × Thickness). Laser process parameters were laser energy of 30 J, square spots of 4 mm × 4 mm, pulse width of 15 ns and continued multiple LSP at the same positions (LSP-1~LSP-8). Surface morphology, surface residual stress, and micro-hardness in depth and cross-sectional microstructure were measured by Super depth 3D microscope system, X-ray diffraction instrument, Vickers indenter and Optical Microscope (OM), respectively. The results indicated that high micro-dent depressions of 197.8 μm and ridges of 130.8 μm were generated after continued LSP-5. Surface compressive residual stress changed into tensile residual stress from continued LSP-4 to continued LSP-5. After continued LSP-5, work soft with low micro-hardness was found in the bottom layer. Continued LSP-5 was the spall threshold of Al7050 mid-thick plates. The researched results can be beneficial to avoid the spall and improve the strengthening effect in an industry application of LSP.

Key words:Al7050 mid-thick plates; Laser shock peening (LSP); Over peening effect; Surface integrity; Internal spall