Experimental studies and modeling of strain rate- and temperature-dependent springback behavior of hot-deformed aluminum alloys

The unloading process of hot-deformed aluminum alloys exhibits obvious strain rate-and deformation temperature-dependent nonlinearity and the springback is generated by internal stress relaxation, which affects the forming accuracy of aluminum alloy components. The strain hardening and dynamic softening during deformation as well as static softening during unloading affect the springback of hot-deformed aluminum alloys. In this study, the homogeneous aluminum alloys samples were used to perform the single-pass isothermal hot compression and unloading tests with different deformation temperatures, loading strain rates and strains. The strain-, strain rate-and deformation temperature-dependent unloading and springback behavior of hot-deformed aluminum alloys were studied. The effects of strain hardening, dynamic and static softening on the springback behavior of alloys were revealed. The relationships between unloading stress, springback strain and instanta-neous tangent modulus in unloading were analyzed. A polynomial-type equation was proposed according to the nonlinear unloading stress-strain curves. The microscopic mechanism of nonlinear unloading of hot-deformed aluminum alloys was also clarified based on the physical mechanism of internal stress relaxation and anelastic strain accumulation. A micro-mechanism-based model was developed to describe the springback and internal stress relaxation in unloading after hot deformation of aluminum alloys. The comparison of calculated unloading curves with experimental results indicates that the proposed polynomial-type equation and developed micro-mechanism-based model can describe accurately the nonlinear springback and stress decay in unloading of hot-deformed aluminum alloys, which provide a prerequisite for analyzing the final geometry and residual stress of precision hot-deformed alloy components.