Determination of pressurizing rate during hot gas forming with integrated heat treatment of Al–Cu–Li alloy: deformation and strengthening behaviors

Hot gas forming with an integrated heat treatment was utilized to form complex-shaped components in one operation that obtain full strength. The effects of the pressurizing rate on the deformation and strengthening behaviors were critical. Free-bulging tests were conducted at different pressurizing rates (0.0088–2.37 MPa/s) to reveal the corresponding deformation and strengthening behaviors of an Al–Cu–Li alloy sheet and for choosing appropriate pressurizing conditions. The profile and thickness were analyzed to describe the deformation behaviors. The Vickers hardness under different pressurizing and deformation conditions was measured to evaluate the strengthening behavior. The microstructure evolution was observed to reveal the deformation and strengthening mechanisms. An excellent bulging ability was obtained under the full solution condition, with a maximum strain of 0.88 at a pressurizing rate of 0.034 MPa/s. The thickness distribution became more uniform under rapid pressurizing conditions because of the increasing strain and strain-rate hardening abilities. The hardness increased with increasing deformation and was not affected by the pressurizing rate. Dynamic recovery was the main deformation mechanism, and dynamic recrystallization occurred at a low pressurizing rate. Fine precipitates comprising the T₁ phase (Al₂CuLi, hexagonal structure) were the main strengthening phase. The pressurizing condition was only considered to obtain the maximum improvement in formability and microstructure, regardless of its effect on strengthening during hot gas forming with an integrated heat treatment.