Prediction of forming limit diagram for pure magnesium tube using hydroforming process modeling

The main objective in this study is to model the hydroforming process for Mg tube and obtain the forming limit diagram (FLD) using finite element method. In the first step, three -dimensional finite element modeling of hydroforming process of AL-7020-T6 tube was performed to plot FLD. In order to identify the appropriate criterion for the onset of necking, the hydroforming process modeling was performed by considering the four criteria including of the second derivative of minimum principal strain, maximum principal strain, thickness strain and equivalent plastic strain. Comparison between simulation and experimental results indicated that the second derivative of minimum principal strain, max principal strain and equivalent plastic strain were appropriate criteria for simulation. After validation of the hydroforming process modeling with experimental result, the FLD of the Mg tube was extracted. The results show that in the loading with different axial feeding, the necking time and the amount of stress and strain change. Therefore, various limit strains are obtained by changing the loading conditions. Also, according to the FLD, the higher ratio of axial feed to internal pressure causes the limit strain shifts to the left in FLD plane.