Yanle Li, Feifei Liu, Heng Chen, Xiaoxia Qi, Tingyu Ge, Xunzhong Guo, Hai Gong, Fangyi Li
• The ductility enhancement mechanisms of the cryogenic uniaxial tension and incremental sheet forming process were unraveled. • The fracture mechanisms of sheet metal under different deformation modes were investigated. • Necking was eliminated in cryogenic uniaxial tension due to the suppression of the Portevin–Le Chatelier effect. • A multi-scale finite element simulation method for incremental sheet forming process has been established. High-strength aluminum alloys are potential structural materials for aerospace and transportation fields. However, the poor formability at room temperature (RT) and the unstable microstructure at elevated temperature limit the wider application in which large plastic deformation is required. In this study, cryogenic tensile tests and incremental sheet forming (ISF) experiments were conducted to investigate the cryogenic ductility enhancement mechanisms under different deformation conditions of AA7075-W alloy. A multi-scale finite element simulation model for ISF was established, providing a novel approach for constructing the constitutive model of ISF. In cryogenic uniaxial tension, the tensile strength increased by 36% and the ultimate strain increased by 60%. In the cryogenic ISF process, the maximum axial forming force increased by nearly 38%, and the maximum forming wall angle was increased from 55° to 60° at the same silimar forming depth, both of which possessed a significant cooperative enhancement effect. In cryogenic uniaxial tensile strain, the sheet ductility enhancement mechanisms include the elimination of necking, the obstruction of crack propagation by impurity phase fragmentation, and the enhancement of geometrically necessary dislocations (GNDs) distribution uniformity. In cryogenic ISF process, the ductility enhancement mechanisms include inhibition of geometrically necessary dislocations growth and the enhancement of work-hardening capacity.