Mechanism of the high elongation but low formability of high-strength aluminum alloy in W-temper

The paradoxical combination of high uniaxial elongation but poor multiaxial formability in W-temper 2219 aluminum alloys presents a long-standing challenge for aerospace forming applications. This study delivers a fundamental advancement by elucidating the underlying stress-state-dependent fracture mechanisms that govern this behavior. Using a hybrid experimental–numerical approach spanning a wide range of stress states, we reveal that the apparent ductility observed in uniaxial tension does not translate to global formability due to the complex interplay between dynamic strain aging (PLC effect), conjugate shear band formation, and the separation of the stress-strain maximum shear planes under large plastic strains. Crucially, we demonstrate that these phenomena induce stress-state-sensitive localization modes that accelerate damage evolution under certain loading paths while retarding it under others. This mechanistic insight bridges a key knowledge gap between microstructural instability and macroscopic formability in solution-treated aluminum alloys. The findings not only explain the failure inconsistency observed across different forming processes but also offer a physics-based foundation for designing better forming strategies and improving the processability of dynamic strain aging-prone aluminum alloys.