Reseach On Microstructure And Properties Of The 6005A-T6/6082-T6 Dissimilar Aluminium Alloy Welded Joints By MIG And FSW

Lightweight is a key for enhancing the performance of railway vehicle recently, and aluminum alloy car body can meet the requirement. The main method for the car body manufacturing are MIG and TIG, and the performance of joints made by fusion welding is low, which is the main cause of influencing safe driving of railways. Friction stir welding is characterized by excellent properties of the welding joint and low welding stress and distortion, and has been applied in the manufacture of high-speed aluminum alloy car body abroad. Composite structure composed of 6005 A-T6 aluminum alloy and 6082-T6 aluminum alloy will contribute to weight and cost reduction and making full use of their advantages. Both of them have good formability, corrosion resistance and weldability, etc. However, there are few reports about the structure and properties of the joints of different chemical composition of aluminum alloy made by FSW, especially the fatigue behavior of the joints.In this study,6005A-T6 and 6082-T6 aluminum alloy with a thickness of 12mm were jointed by friction stir welding and fusion welding, respectively.6005A-T6 was placed at the advancing side and 6082-T6 was placed at the retreating side in FSW, according to the design of the actural production, the joint is butt-lap, and multi-pass welding was adopted in MIG. Microstructure and mechanical properties of MIG and Friction Stir Welded joints were investigated by optical microscope, tensile test, Vickers hardness tester.Tensile and fatigue fracture morphology were studied by SEM, beyond that, the relationship between fracture morphology and fracture mechanism was discussed in detail.Studies have shown that equiaxial crystal grain is formed in the nugget zone (NZ), and the average size is 12.4 u m. The grains in the thermo-mechanically affected zone (THAZ) have been elongated, and the grains in the heat affected zone (HAZ) grew up obviously. The weld-metal of MIG is obvious casting structure, and the average size of the grain is 61.4 μm. The situation of grains growing up in HAZ is serious than that of FSW. Both the HAZ of the joints made by FSW and MIG have been softened, and the situation at the retreading side of the joint made by FSW is more serious than that of the advancing side. In the case of high circle fatigue (Nf>107), the fatigue strength of the joints made by FSW and MIG is 146Mpa and 125Mpa, respectively. The fatigue strength of the joints made by FSW is 14% higher than that of MIG.