Multi-objective optimization of the process combining ultrasonic vibration and age-forming of dissimilar friction-stir-welded Aluminium T-stiffened plates

This paper innovatively proposes a combined process combining ultrasonic vibration (abbreviated UV) with creep age forming (abbreviated CAF), named UVCAF, for high-quality forming of dissimilar 7055-T6/2197-T8 FSWed T-stiffened plates. And based on this, a multi-objective optimization quality comprehensive evaluation model of the AMOGA-EWM algorithm is proposed, obtaining the optimal process parameter solution combination as [164.8 °C, 9.2 h, 9.6 μm]. The reliability and feasibility of the above evaluation model in improving the forming rate and mechanical properties for the T-stiffened plates are verified. Meanwhile, through comparative analysis of the experimental results of UVCAF under the optimal process parameters, it is found that the forming rate, tensile strength, and elongation of T-stiffened plates under UVCAF are 5.4%, 12.3 MPa, and 0.82% higher than those under CAF. In addition, the microscopic analysis results indicate that the fracture mode of the specimens under CAF and UVCAF is a ductile fracture, and the weld nugget zone of the specimens under CAF and UVCAF is the combined reinforcement of the T1 and η phase. However, the introduction of UV through the strengthening effect of fine grains makes the η phase more abundant in UVCAF specimens, thereby improving the forming accuracy and performance of the specimens.