Forming limit of AZ31 alloy sheet and strain rate on warm sheet metal forming

The warm formability of AZ31 sheet has affected with strain rate as well as temperature because elongations are changed by the temperature and strain rate at an elevated temperature. Therefore, the formability must be investigated with the effects of both strain rate and temperature. In this study, the effects of temperature and strain rate were investigated on square cup drawing by the experimental and FE analysis. And, the uni-axial tensile test and stretching test by the hemi-spherical punch were performed to analyze causes of forming limits for various forming conditions.AZ31 alloy sheet shows increased total elongation by increasing the deformation temperature from 200 to 400 °C on uni-axial tensile test. The uniform elongation decreased by increasing the temperature and increased by the increasing the strain rate. On the other hand, the post-uniform elongation increased with higher temperature and lower strain rate. Forming limit by FLD test was worse on higher strain rate. Also, the failures were occurred frequently at high forming speed on square cup deep drawing. After all, the forming limit was dependent with the post-uniform elongation more than uniform elongation. Finally, the effect of strain rate must be considered on the FEM analysis. Therefore, the viscoplastic material model and strain rate-dependent FLD curve were used to simulate forming process and predict the failure. The simulated results show good agreement with the experimental results.