Fatigue crack propagation of 7050 aluminum alloy FSW joints after surface peening

The surface composite modification of the 7050 aluminum alloy friction stir-welded joints was performed by shot peening(SP)/multiple rotation rolling(MRR) and MRR/SP, and the fatigue performance of the nugget zone(NZ) was investigated. The results demonstrated that the fatigue life of SP/MRR samples is longer than that of MRR/SP . On the plane 150 μm below the surface. The grains with high angle grain boundary account for 71.5% and 34.3% for MRR/SP and SP/ MRR samples , respectively. The crack propagation path of the MRR/SP is transgranular and intergranular, and it is intergranular for the MRR/SP. Multitudinous fatigue striations and some voids appeared at the fracture during the stable crack propagation stage.However, fatigue striations for SP/MRR are with smaller spacing, fewer holes, and smaller size under SP/MRR compared with fatigue fracture of MRR/SP. The differences in fatigue properties and fracture characteristics of the NZ are related to the microstructure after the two combined surface modifications.