Deformation behavior of Al–Cu–Mn alloy sheets under biaxial stress at cryogenic temperatures

A research on the deformation behavior of Al–Cu–Mn alloy sheets was conducted under a biaxial stress state at cryogenic temperatures to determine fundamentals of a novel forming method for complicated components. The strength, ductility, strain hardening exponent and work hardening rate of an Al–Cu–Mn alloy sheet were compared with uniaxial tension tests at different cryogenic temperatures. The deformation of a dome specimen was analyzed by using a newly-designed bulging device and an optical three-dimensional (3D) deformation measuring system at temperatures of 293 K and 113 K. The limiting dome height (LDH) at 113 K was 37.1% higher than that at 293 K. The strain and thickness distribution of the bulged specimens were more uniform at 113 K owing to a higher strain hardening capacity. Compared to room temperature, the cryogenic bulging results revealed that the formability of the Al–Cu–Mn alloy could be enhanced under a biaxial stress state. Likewise, the resistance to the micro-deformation of the aluminum alloy was increased due to the harder formation of the slip bands and fewer slip localizations at cryogenic temperatures. The increased dislocation density and strength of the alloy were resulted from numerous netted dislocation substructures with interactive dislocation walls (DWs) and dislocation tangles (DTs). Furthermore, more uniformly distributed dislocation cell structures with continuous ridges could facilitate multiple dislocation glides and diminish localized deformation, which resulted in the improvement of the ductility of the Al–Cu–Mn alloy during the cryogenic deformation process.