## 1 Introduction
It was found that reducing the post-quench delay resulted in lower magnitude residual stresses as the aluminum alloy underwent natural aging during the delay, which changed the work hardening behavior of the alloy during subsequent cold compression. [PERSON] [15] investigated the influence of the cooling rate on the residual stress and tensile properties of 2A14 aluminum alloy by numerical simulation and quenching experiments. Lower cooling rates reduced the tensile strength and yield strength due to a decreased amount of fine precipitates, and reduced the residual stress with the reduction of plastic strain and the degree of inhomogeneous plastic deformation. [PERSON] [16] established a dislocation density-based model for accurate prediction of residual stress for as-quenched Al-Cu-Mg alloy, which considered the influences of precipitation, solid solution and forest dislocation. The results showed that volume fraction of precipitates decreased with the increasing temperature and cooling rate, in contrast to the increasing trend for the radius of precipitates. The quench-induced precipitates had an influence only on the magnitudes of flow stress at low temperatures. Cold compression [17] was adopted to relieve the quenched residual stress by many researchers, which played a significant role in the reduction of residual stress. [PERSON] [18] used the cold compression stress relief process to reduce the quench-induced stresses in high-strength aerospace aluminum alloy forgings. However, this method did not completely relieve the stress, and the overall reduction of peak stress magnitudes was approximately 43-79%. [PERSON] [19] investigated the effect of cold compression deformation on the distribution of quenching residual stress of 7A85 aluminum alloy thick block forging. The experimental results indicated that the optimal compression deformation value was 1-2%, which reduced 70% of the residual stress for the specimens. [PERSON] [20] determined the residual stresses through the thickness of quenched and quenched followed by cold compressed 7050 aluminum alloy using the contour method and neutron diffraction. The longitudinal residual stresses obtained by the two techniques achieved good agreement in both trend and magnitude in both the quenched and cold compressed components. Exceptfor the cold compression, cold stretching was also effective in reducing the residual stress of the components with simple geometry. [PERSON] [21] used two different methods of cold working (compression and stretching) to reduce the residual stress and the results showed that both compression and stretching processes reduced the residual stresses more than 90%. However, the effect of deformation in compression and stretching on the residual stress variation was different [22]. Due to the limitations in the capacity of the cold compression machine, integral cold compression could not be conducted for the components with large size; therefore, multiple cold forging operations were adopted for the components with the larger size. [PERSON] [23] studied the effect of the compression ratio, friction coefficient, length of overlap and length of the T-section component on the residual stress distribution during the multiple cold forging operations. A percentage reduction in the peak residual stress of over 90% was found and the optimal parameters for residual stress relief by cold compression had been obtained. Large tensile residual stresses generated during cold working processes could negatively affect the integrity and geometric accuracy of the workpiece, and the heat treatment was adopted for the reduction of residual stress [24]. [PERSON] [25] proposed a novel residual stress relaxation model considering the dislocation evolution mechanism and the plasticity theory to predict the change of residual stress during the annealing process. The aging heat treatment partially relieved the residual stresses generated at previous stages of forging and water quenching; however, the stress field would not be completely relaxed [26].