Springback analysis of Z & T-section 2196-T8511 and 2099-T83 Al-Li alloys extrusions in displacement controlled cold stretch bending

The aluminum-lithium (Al-Li) bent extrusion products offer opportunities for significant improvements in structural performance due to its lightweight material and component. However, the high ratio of strength to Young's modulus may induce significant elastic recovery after unloading. The precise bending of the Al-Li alloys extrusion depends on the understanding of the springback features and mechanisms of the profile stretch bending process, which is a much complex physical process with multi-factors coupling interactive effects. For this purpose, the springback behaviors of the age-hardened 2196-T8511 and 2099-T83 Al-Li alloys extrusions with Z-section and T-section under displacement controlled cold stretch bending (DCSB) are investigated. Firstly, an analytical model is developed based on the radius of strain neutral layer and verified experiments are carried out. Secondly, the connector element in FEM is used to simulate DCSB. Furthermore, the roles of material, radius, process parameters and friction condition are revealed. Finally, springback control method is proposed to ensure the stabilization and precision of bending parts. The results show that: (1) The analytical model and finite element method can be used to evaluate effectively the effects of material and process parameters on springback of Al-Li alloys extrusions in DCSB. (2) 2196-T8511 and 2099-T83 Al-Li alloys extrusions show significant springback at room temperature because of its higher strength to Young's modulus. (3) Increasing pre-stretching or post-stretching strain can significantly reduce the radius springback and time-dependent springback of 2196-T8511 and 2099-T83 Al-Li alloys extrusions, but it is limited by the lower fracture strain. (4) The lubricant between extrusions with die reduces the stable radius springback ratio greatly for Al-Li alloys in the T8 temper.