Evolution and formation mechanism of residual stress in Al-Cu alloy rings during ring rolling and quenching

The large-scale ring components, as thin-walled structures, are prone to unpredictable machining deformation due to the initial residual stresses introduced by rolling and quenching, which seriously affect the dimensional accuracy and service life of the ring components. Therefore, the relief and homogenization of residual stress inside large-scale ring components is crucial. However, the existing studies rarely involve the essential causes and the evolution laws of residual stresses during the manufacturing of ring components, which are indispensable for understanding the failure mechanisms of components caused by residual stresses and specifying relevant protective measures. Therefore, the evolution and distribution laws of stress-microstructure-property non-uniformity during the hot forming (ring rolling) and heat treatment (quenching) of 2219 AlCu alloy rings were precisely and deeply explored using scaled experiments in this paper. The relationship between non-uniform deformation and residual stresses was analyzed, and the basic equation that residual stresses must satisfy was established. Furthermore, the concept of the "noncoordination coefficient" was proposed, revealing the physical mechanism of residual stresses induced by non-uniform deformation. In addition, the influencing factors and formation mechanisms of residual stresses in the rolled and quenched state of rings were studied, and the essential reasons for the differences in residual stresses between the rolling and quenching processes were obtained. The experimental results indicate that the circumferential and axial residual stresses increased from 1.48 and 0.51 MPa to -142.68 and -122.31 MPa, respectively. The standard deviation changed from 13.47 and 33.52 MPa to 63.42 and 61.61 MPa, respectively. The maximum range of tensile strength, yield strength and elongation rates of the rolling and quenched state is 12.82 and 20.16 MPa, 17.49 and 22.14 MPa, and 8.62 % and 7.56 %, respectively. All fractures are microporous aggregation ductile, including dimple transgranular fracture and intergranular fracture. The quenched state exhibits a significantly larger grain size compared to the rolled state. The appearance of residual stress is essentially to force the inconsistent deformation of various parts inside the object to maintain its integrity and continuity, which leads to a local mismatch of micro-elements inside the ring and further induces nonuniform strain and stress. The difference in the severity of "penetrability" induced by different temperature gradients determines the difference in residual stress between rolled and quenched rings, larger rings have higher and more non-uniform residual stress than smaller rings under the