Prediction of material behavior during biaxial stretching of superplastic 5083 aluminum alloy

In order to predict the flow behavior of a superplastic Al-Mg alloy sheet under near biaxial tension mode, finite element simulation was performed using commercial FE software (ABAQUS). To capture the time-dependent plastic behavior of the material, three constitutive models, i.e., the Voce model, a power law, and a newly introduced variable m value viscoplastic (VmV) model, were implemented in FE simulations. The models’ parameters were assessed from the three uniaxial stress-strain curves ranging from 10−3 to 10−1 s−1. To validate the simulation results, Nakazima hemispherical dome testing was performed under isothermal conditions using a constant strain rate of ~ 0.01 s−1 at 450 °C. After the tests, the thickness of the deformed parts was measured and the volume fractions of cavities at different locations were assessed using X-ray micro-tomography, and the impact of the strain path on the rate of cavitation was discussed. Based on the obtained results, when the material behavior was modeled using the VmV model, the accuracy of the prediction was about 2 and 5 times better than the ones from power law and Voce model, respectively. It was also observed that the volume fraction of the cavities exponentially increases with equivalent plastic strain and it depends on the strain path history.