Experimental and simulation investigation on thermal-vibratory stress relief process for 7075 aluminium alloy

Residual stresses evidently affect the strength, fatigue property and machining deformation of the mechanical components. Therefore, stress relief processes are extensively applied in the manufacturing to enhance the mechanical properties of products. In this study, seven 7075 aluminium alloy specimens are treated by thermal- vibratory stress relief (TVSR), thermal stress relief (TSR), and vibratory stress relief (VSR). Finite element (FE) models considering the stress relaxation effects and transient periodic vibration loads are proposed to simulate the TVSR, TSR and VSR process. The residual stresses before and after the processes are measured and compared, and the effectiveness of the FE models is validated. Scanning electron microscope (SEM) and transmission electron microscope (TEM) are used to observe the microstructure and crystal dislocation, respectively. Results show that TVSR can evidently reduce the residual stress in aluminium alloy, and the stress relief rate of TVSR for the peak stress are 20.43% and 38.56% higher than that of TSR and VSR, respectively. It also found that TVSR has no obvious influence on the grain size, but evidently increase the dislocation density. Eventually, the stress relief mechanism of TVSR is analyzed and summarized.