Research on Creep Deformation of Dissimilar FSWed T-Joints Under Different Ultrasonic Vibration Modes: Experiment, Constitutive Model, and Simulation Verification

This article presents experimental and numerical studies on the creep deformation of 7055-T6 Al and 2197-T8 Al-Li T-joints. Firstly, the optimal process parameters for creep tensile tests (CATs) are determined to be 155 °C, 130 MPa, and 8 h. Based on this, different modes of ultrasonic vibration are introduced. It is found that under the same amplitude, the creep limit of intermittent vibration is 64.7‰ to 97.2‰ higher than that of continuous vibration, and the tensile strength of the former specimens is significantly better than that of the latter. Further analysis reveals that during long-duration or high-amplitude vibrations, the joint material exhibits hardening effects, while short-duration, low-amplitude intermittent vibrations result in softening effects. When the amplitude is 12.53 μm, the material exhibits optimal comprehensive mechanical properties, with yield strengths, tensile strengths, and elongations of 402.1 MPa, 429.3 MPa, and 7.9%, respectively. Additionally, based on the mechanisms of superposition and acoustic softening effects, an improved creep aging constitutive model is established, which incorporates the creep process, stress superposition, and ultrasonic softening changes and is applied in ABAQUS. It is found that at an amplitude of 12.53 μm, the residual stress in the joint is more thoroughly eliminated and distributed more evenly, measuring 97.35 MPa. Moreover, the creep strain calculated using the above model in a finite element analysis shows a high degree of agreement with the experimental results, indicating that the proposed model can more accurately predict the creep deformation behavior of FSWed T-joints during the CAT process.