Study On Fatigue Behavior Of FSW And TIG Butt Joints Of 7075/6061 Aluminum Alloy

As a light metal,aluminum alloy is widely used in automobile,aviation and other fields.With the rapid development of industry,it is inevitable that there will be connections between dissimilar materials.Due to the difference between the physical and chemical properties of the two materials,it is difficult to use the traditional fusion welding technology to weld the materials.The emerging friction stir welding(FSW)can solve the connection problem of dissimilar aluminum alloys,and the fatigue problem under the cyclic working load is increasingly prominent.In this paper,the fatigue properties of 6061 and 7075 aluminum alloy friction stir welding butt joints were studied,and the fatigue life was predicted.The main work content of the paper is as follows:1.The macroscopic morphology and microstructure of the weld cross-section of the stir friction welded butt joint of dissimilar aluminum alloys were observed using an optical microscope to analyze the effect of the welding process on the surface and the organization of each region.A universal testing machine was used for static mechanical testing of the welded parts,and then a servo-hydraulic fatigue testing machine was used for constant amplitude loading fatigue testing of the welded parts,and the S-N curve of the welded joint was fitted to analyze the relationship between fatigue life and load.The use of scanning electron microscopy on the fatigue damage to the specimen fracture observation,analysis of fatigue fracture mechanism and the characteristic morphology of each fracture.2.According to the fatigue test data of the stir friction welded specimens,the finite element method was used to analyze the stress-strain of the welded joint and to predict the fatigue life of the welded joint in combination with the fatigue life prediction method.The relevant finite element model is established,and the fatigue life is estimated using the Smith-Watson-Topper(SWT)damage model of the critical distance method of the point and line method with the local stress strain method and the modified Manson-Coffin(MC)damage model.The predicted results are compared with the experimental results to analyze the applicability of the point and line methods with the SWT damage model and the modified MC damage model.3.Macroscopic morphological and microstructural observations,static mechanical tests and constant amplitude loading fatigue performance tests and fatigue fracture analysis were performed on the heterogeneous aluminum alloy argon arc welded butt joints.Through stir friction welding specimens and tig welding specimens through the tensile test and constant amplitude loading fatigue test,analysis of the mechanical properties of the two specimens and fatigue properties,fatigue fracture observation and analysis of the fracture mechanism of the two types of welded joints and fracture characteristics of the morphology.