An investigation of enhanced formability in AA5182-O Al during high-rate free-forming at room-temperature: Quantification of deformation history

The goal of this work is to improve our understanding of formability enhancement in aluminum (Al) sheet alloys that has generally been observed during high-strain-rate forming. In the work presented here, experiments and numerical modeling were used to investigate the room-temperature formability of AA5182-O Al alloy sheet (1 mm thick) at high strain-rates using the electro-hydraulic forming (EHF) technique. A finite element model, using Johnson-Cook constitutive equation, was developed to simulate the high-rate forming behavior of Al under EHF and test samples were designed to obtain different strain paths at the apex of the EHF domes. The deformation history of Al sheets, under free-forming conditions and inside a conical die, was experimentally determined and compared to the model predictions. Experimental data shows that the high-rate formability of AA5182-O Al at minor strains of ∼−0.1 and ∼0.05, relative to its corresponding quasi-static formability, was enhanced locally by ∼2.5× and ∼6.5× under free-forming and when forming inside the conical die, respectively. The in-plane peak engineering strain-rate associated with the enhanced formability during free-forming was measured to be ∼3900/s while the pre-impact strain-rate during conical-die forming was estimated to be ∼4230/s. The strain-path associated with enhanced formability was experimentally determined under a free-forming case and was found to be in good agreement with that predicted by the numerical model. To the authors' knowledge, these results are the first to experimentally quantify the deformation history associated with enhanced formability that has often been reported in the literature.