Abstract Machining deformation caused by the release of residual stress during the processing of large-scale 7050 aluminum alloy thin-walled components remains a critical bottleneck, limiting high-quality and high-precision manufacturing and significantly compromising the dimensional stability of the parts. As a novel stress-control technique, ultrasonic treatment has been proven effective in improving the residual stress distribution within aluminum alloys, thereby reducing the machining deformation of thin-walled structures. However, a systematic analysis of the dynamic evolution and underlying release mechanisms of residual stress under ultrasonic action is still lacking. To analyze defect evolution and the origins of milling-induced residual stress, a molecular dynamics model of milling for 7050 aluminum alloy containing η-phase (MgZn₂ precipitates) was constructed. Following the simulation of the stress release process under ultrasonic treatment, our results reveal that the reduction and homogenization of residual stress are fundamentally attributed to dislocations absorbing energy within the applied ultrasonic field. This energy absorption activates dislocations, enabling them to overcome the potential energy barrier for motion. Consequently, extensive annihilation reactions occur primarily among Shockley partial dislocations, leading to a decrease in the total dislocation density. Ultimately, the internal stress of the material is relaxed and released through plastic deformation mediated by these dislocation reactions.
Song et al. (Fri,) studied this question.