Research on joining mechanism and fracture mode of Al-Cu alloy joint by refill friction stir spot welding

Research on joining mechanism and fracture mode of Al-Cu alloy joint by refill friction stir spot welding

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In order to increase the joint strength, RFSSW is used to weld 2524-T3 aluminum alloys of aircraft skin.The joint Connection Mechanism is studied through the analysis of its appearance and microstructure by SM and metallographic microscope, The mechanical properties of the joint is investigated by tension-shear test and cross-tension test, and the fracture is analyzed by SEM.The experiment results show that the RFSSW joint has a good forming and defect-free on the surface, and with the action of thermo-mechanical, the cross-section of the joint can be divided into four zones in grain structure.The mechanical performance of RFSSW joints is generally higher lovesense 3 than that of riveting joints.

The tension-shear performance of welding joints reaches 7.233 kN, which is 113.4% higher than that of riveting joints.The tension-shear performance of welding joints reaches 3.

172 kN, which is 6.16% higher than that of riveting joints.There are two types of joint fracture modes: nugget debonding fracture and plug fracture.When the plunge depth of sleeve is relatively small flex 4 heartworm test and the internal agitation of joint is insufficient enough, it can result in the nugget debonding fracture.

With the increase of plunge depth of sleeve, plug fracture make gradually changes, the transition from plug fracture (fracture in the upper sheet) to plug fracture (fracture in the lower sheet).Ductile fracture is observed in both tension-shear test and cross-tension test with the nugget debonding fracture.The mechanical properties of refilled friction stir spot welding joints are analyzed, which provides theoretical and technical basis for the application of RFSSW in aerospace structural components.