Monolithic thin-wall components of 2219 Al–Cu alloy are widely used in aerospace and military fields, and usually treated with solution and quenching to improve their comprehensive performance. However, a high magnitude residual stress is introduced into the components during the quenching process, which is unfavorable to the subsequent manufacturing process and service performance. Therefore, residual stress relief is essential to enhance the performance of the components. A conventional effective method is thermal stress relief (TSR). However, the underlying mechanisms of TSR still remain unclear and lack a quantitative interpretation. In the present work, the evolution and distribution laws of the residual stresses, tensile properties, Vickers hardness, dislocations, precipitated phases, and metallography during TSR were investigated. Based on the experimental results, dislocation theory and strengthening mechanisms were applied to reveal the underlying mechanisms of the residual stress relief by TSR. The results showed that the circumferential and axial residual stress relief rates can reach 86.37 and 85.77% after TSR, respectively. The residual stress relief after TSR is attributed to the dynamic evolution of dislocation configuration and density. The improvement in the mechanical properties mainly depends on the precipitated phases and is also affected by the stress orientation effect caused by the residual stress.

Vibratory stress relief (VSR) is a highly efficient and low-energy consumption method to relieve and homogenize residual stresses in materials. Thus, the effect of VSR on the fatigue life should be determined. Standard fatigue specimens are fabricated to investigate the fatigue life of Ti-6Al-4V titanium alloy treated by VSR. The dynamic stresses generated under different VSR amplitudes are measured, and then the relationship between the dynamic stress and vibration amplitude is obtained. Different specimen groups are subjected to VSRs with different amplitudes and annealing treatment with typical process parameters. Residual stresses are measured to evaluate the stress relieving effects. Finally, the fatigue behavior under different states is determined by uniaxial tension–compression fatigue experiments. Results show that VSR and annealing treatment have negative effects on the fatigue life of Ti-6Al-4V. The fatigue life is decreased with the increase in VSR amplitude. When the VSR amplitude is less than 0.1 mm, the decrease in fatigue limit is less than 2%. Compared with specimens without VSR or annealing treatment, the fatigue limit of the specimens treated by VSR with 0.2 mm amplitude and annealing treatment decreases by 10.60% and 8.52%, respectively. Although the stress relieving effect is better, high amplitude VSR will lead to the decrease of Ti-6Al-4V fatigue life due to the defects generated during vibration. Low amplitude VSR can effectively relieve the stress with little decrease in fatigue life.

Thermal stress relief (TSR), vibration stress relief (VSR), and thermal and vibratory Stress relief (TVSR) have all been proven to be effective for residual stress relief. So far, no comparison has been made between the effects on residual stress relief of these three stress release methods. In this study, twelve 2219 aluminum alloy welding samples were divided into four groups. One of the groups is used as a reference without any stress relief treatment. The other three groups were processed by TSR, VSR, and TVSR, respectively. The residual stresses of depths of 0–1.2 mm are measured. Results show that small and uniform stresses are observed in the 2219 aluminum alloy welding samples after TSR, VSR, and TVSR treatment. TSR treatment decreased the peak residual stress much more than VSR and TVSR treatment. The maximum reduction of the peak residual stress is 50.8% (210 °C) in the transversal direction and 42.02% (185 °C) in the longitudinal direction after TSR treatment with the temperature range 140 °C to 210 °C. In terms of residual stress homogenization, although the TSR treatment has an advantage perpendicular to the weld direction, the effect parallel to the weld direction is not ideal. The TVSR has a good effect in both directions.