Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy Wing Skin Panels during Bending Forming and Creep Aging Forming

The microstructural evolution and strengthening mechanisms of Al-Zn-Mg-Cu alloy wing skin panels during bending forming and creep age forming (BFCAF) were investigated, with emphasis on the heterogeneity between thin and thick plate regions. The results show that BFCAF does not significantly alter the grain morphology, while deformation heterogeneity leads to distinct microstructural characteristics. The thick plate region undergoes plastic deformation during bending, resulting in higher dislocation density and work hardening, whereas the thin plate region is dominated by creep deformation with a more uniform and recovered dislocation structure. Compared with the pre-aged condition, the BFCAF process leads to an overall improvement in mechanical properties, with the yield strength of the thin and thick plate regions increasing by 11.3 and 18.5%, respectively. During creep aging, dislocation rearrangement promotes stress relaxation, leading to a low residual stress level (− 122 to 50 MPa). Meanwhile, the higher dislocation density in the thick plate region enhances precipitation, with the average η′ precipitate size increasing by 1.20 times. A strength model reveals that the superior mechanical properties of the thick plate region are mainly attributed to the combined contributions of dislocation strengthening and precipitation strengthening, with an increment of 34.2 MPa in precipitation strengthening. These results highlight the critical role of deformation-induced dislocation heterogeneity in regulating precipitation behavior and mechanical properties during BFCAF process.