Cyclic stress and strain responses of AZ31 magnesium alloy sheet metal at elevated temperatures

Lightweight materials have been widely and increasingly utilized for the automotive industry to reduce the carbon dioxide (CO2) emissions. To replace the existing ordinary steels, the automotive companies have been investigated the other materials to satisfy the specific strength, stiffness and recyclability. Under these circumstances, some researchers have been paying attention to the magnesium alloy sheets. Although the material have low ductility at room temperature due to small number of slip systems, it is the well-known fact that the formability at the elevated temperatures around 200 ºC is drastically improved. In these days, the local heating techniques have been applied to the press forming systems in order to realize the power saving manufacturing systems in spite of the existing systems. Although the warm stamping has some great advantages to improve the formability, the prediction of the deformed sheet metal is not always enough accurate. In order to investigate the stress strain responses for the material at the elevated temperatures, a testing device which can observe the cyclic stress strain responses was developed in the present research. The magnesium alloy sheets were warmed at around 200 ºC to reduce the critical resolved shear stress of slip systems and improved its deformability. The corresponding stress strain responses by finite element method based on the crystal plasticity were calculated. It was found that the calculations could capture the above-mentioned features very well.