Analysis of Tensile Fracture Mechanism of 2219 Aluminum Alloy Friction Stir Welded Joints

doi:10.3901/JME.260113

Abstract

Abstract: The microstructural inhomogeneity in friction stir welded joints has been shown to lead to diversified tensile fracture locations and fracture mechanisms under varying conditions, while investigations into the tensile fracture mechanisms of these joints have been limited. In order to reveal the tensile fracture mechanism of friction stir welded joints in 2219 medium-thick plates, friction stir butt welding was performed on 6 mm thick 2219 aluminum alloy plates. Hardness testing and tensile testing are conducted on the welded joints, and the fracture surfaces are analyzed using metallographic examination, scanning electron microscopy(SEM), and electron backscatter diffraction(EBSD). The results indicate that the lowest hardness is observed in the thermomechanically affected zone on the advancing side(AS-TMAZ) of the welded joint. The digital image correlation(DIC) test results of the tensile test have been shown that when the engineering strain of the welded joint tensile specimen is less than 8.34%, the maximum principal strain is observed to occur in the joint area AS-TMAZ and thermomechanically affected zone on the re-treating side(RS-TMAZ). When the engineering strain exceeds 8.34%, the region of maximum strain is transformed to the AS-TMAZ of the joint, and fracture is propagated at an angle of approximately 45° near this region. The morphology of the initial fracture region is characterized by large dimples separated by tear ridges, while the morphology of the final fracture region is dominated by large cleavage facets and smaller dimples. The fracture mechanism of the joint exhibits a mixed ductile-brittle fracture behavior. Due to the obvious orientation of the second phase in TMAZ, the deformation coordination ability in this region decreases. In the TMAZ, the grains are deflected and elongated under stress, and stress concentration is induced due to the significant difference in grain size compared to the heat-affected zone (HAZ). The dislocation density from TMAZ to HAZ drops sharply, and the welded joint ultimately fractures at the junction of AS-TMAZ and AS-HAZ. The above research results can provide technical references for optimizing welding conditions, controlling joint microstructure, and improving mechanical properties.

Key words: 2219 aluminum alloy, friction stir welding, uneven distribution, microscopic organization, fracture mechanism

CLC Number:

TG456

LI Qun, CAO Bo, JIANG Yan, CHEN Lijie, HU Jianliang, CHEN Lei. Analysis of Tensile Fracture Mechanism of 2219 Aluminum Alloy Friction Stir Welded Joints[J]. Journal of Mechanical Engineering, 2026, 62(4): 148-156.

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