Improvement in fatigue properties of 2024-T351 aluminum alloy subjected to cryogenic treatment and laser peening

The aim of this study was to investigate the effects of Cryogenic Treatment (CT) and Laser Peening (LP) on the fatigue properties of 2024-T351 aluminum alloy. The measurements of tensile properties and microhardness were carried out, and the residual stress tests were also conducted through x-ray diffraction (XRD) technology. Examination of microstructure was executed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Fatigue tests were conducted and the fatigue fracture morphologies were also analyzed by SEM. Experimental results found that both CT and LP could enhance the fatigue properties of 2024-T351 aluminum alloy. The process of CT prior to LP could provide a higher fatigue life compared with single CT or LP process. After CT prior to LP, the fatigue life of the treated specimen was 28,077 cycles under gradient loading, which obtained an increase of 4640 cycles compared to the untreated specimen. Meanwhile, compared with single CT and LP, CT prior to LP could produce finer grains, more precipitated second phases, higher density dislocation and compressive residual stresses. Beneficial microstructure evolution and compressive residual stress induced by CT prior to LP were considered to be the main factors that contribute to the improvement of the fatigue properties.