The effect of laser shock peening on very high cycle fatigue properties of laser welded 2A60 aluminum alloy joints

Abstract

Laser shock peening (LSP) technology has the advantages of deep residual compressive stress field, low degree of cold hardening and controllable hardening area. The surface modification of welded structures has broad prospects. To predict the very high cycle fatigue (VHCF) life of an aero engine impeller, it is of great engineering significance to study the VHCF performance of 2A60 aluminum alloy. The effects of LSP on VHCF properties of laser welded joints were investigated from the S-N curve, fracture morphology, residual stress, hardness, and roughness. The results show that the S-N curves of the 2A60 aluminum alloy matrix under the condition of ethanol cooling belong to the infinite life type. The S-N curves of welded and LSP samples belong to the continuous decline type. In the process of LSP, the fatigue crack source is transferred from the surface of the sample to the second surface of the sample, which not only counteracts the residual tensile stress introduced on the surface of the sample during welding but also introduces considerable residual compressive stress on the surface of the sample. The roughness is reduced, thus improving the fatigue stsample's fatigue strength and life. The strengthening mechanism of LSP is discussed from two aspects of dislocation strengthening and residual stress. The LSP results in many dislocation proliferation within the grain, and the dislocation entanglement and dislocation wall are formed among the dislocations. The original coarse crystal is divided into multiple subgrains to achieve the effect of grain refinement. Grain refinement and high-density dislocation increase the hardness of the material.