| With the characteristics of high specific strength and low density,6061-T6 aluminum alloy has been widely used in the car body manufacturing of metro and high-speed EMU.As a kind of green solid phase connection technology,friction stir joining,plays an important role in aluminum alloy connection.As the speed of the vehicle accelerates,higher performance is required for the joint area.Among them,As the primary factor to maintain the integrity of the vehicle under high-speed impact,impact resistance is responsible for the safety of the driver and passenger.In this paper,through changing the linear connection trajectory of the friction stir joint to a swinging S-type joining track,we found that the impact toughness and salt spray corrosion resistance of the joint area are effectively improved,and the mechanical properties and formation of the connection area under the S-type joining track are improved.The mechanism is studied to explore the influence of the swing radius on the performance of the joint area.1)The tool adopts a shaft shoulder with a concentric concave ring size of 24mm,and the length of the tapered threaded pin is 9.8mm.When the joining parameter spindle speed is 500r/min?1000r/min and the joining equivalent speed is 70mm/min?130mm/min,the rolled 6061-T6 aluminum alloy with a thickness of 10mm can obtain a joint without obvious defects under different joining track.2)Under the joint parameter of equivalent joining speed of 70mm/min,the impact toughness of the joint area of the linear track is up to 73.81J/mm2 when the spindle speed is 1000r/min,and the impact toughness of the joint area of the S-type track is 80.87J/mm2.About 10%;when the spindle speed is 700r/min,the impact toughness of the S-shaped track joining area is up to 94.64J/mm2,that is,the S-type track can effectively improve the impact toughness of the joint area.3)The metal flow pattern inside the friction stir connection area of the S-type track can be explained using the "mortise and tenon migration extruding-swing cascade" model,And along the joining direction to form a "thousand layers of cake"like structure,layer and layer in mortise and tenon joint,The thickness of the monolayer plasticized metal is about twice the swinging radius.The bonding strength and the volume and distribution of solute atom clusters at the bonding interface are the main factors affecting the performance of the joint area.The impact fracture process of the "thousand-layer cake" like structure is impact-cushioning energy absorption-impact,prolonging the impact time,and a slight slip occurs between the layers,thus effectively improve the impact toughness of the joint area.4)On the premise of ensuring good overall mechanical properties,it is optimized that the S-type track joint parameters are the spindle speed of 500r/min and the equivalent joining speed of 130mm/min.Under this joint parameter,the swing radius is set to 0.25mm,0.5mm,0.75mm,and 1mm respectively,and the joint test is performed.The tensile strength of the joint area with the increase of the swing radius is almost unchanged to 203Mpa,which is 67%of the base material.The trend of decreasing after increasing,the maximum is 80.74J/mm2 when the swing radius is 0.5mm,which is 2.87 times of the base material,the fracture form is the mixed toughness-plastic fracture,and the salt spray corrosion resistance of the joint area is the best.Figure[42]table[6]reference[81]... |
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