Magnesium (Mg) alloys are the lightest metals that can be used for structural components, and the press forming of Mg alloy sheets has recently attracted attention in automobile and electrical industries. To increase the number of applications of the press forming, it is crucial to understand mechanical properties of Mg alloy sheets. Because Mg alloys are hexagonal close-packed (hcp) materials, mechanical properties of Mg alloy sheets are significantly different from those of conventional structural sheet metals that have cubic structures. Crystal plasticity models can analyze numerically the interaction between mesoscopic crystalline and macroscopic deformation in metals; thus the models are powerful tools to further understand the mechanical properties of Mg alloy sheets. In the present study, the nonlinear response that arose during unloading under in-plane compression of a rolled magnesium alloy sheet was investigated using a crystal-plasticity finite-element method, focusing on the effects of twinning and detwinning. The mechanism that the nonlinear response was more pronounced under in-plane compression than that under in-plane tension was also discussed. In the simulation, a twinning and detwinning model that has originally been proposed by Van Houtte (1978) and recently extended to the detwinning process by the authors [Hama and Takuda, 2012] was employed. From numerical experiments, it was confirmed that, as already pointed out in literature, the activity of detwinning played an important role on the nonlinear response during unloading. On the other hand, it was also found that the basal slip systems could be very active during unloading because of the dispersion of crystal orientations owing to the activity of twinning during loading, which increased the nonlinear response. It was concluded that the nonlinear response during unloading was more pronounced under in-plane compression than that under in-plane tension owing to these two factors that did not present under in-plane tension.
Crystal Plasticity Simulation on Prediction of Macroscopic Mechanical Properties of Metals Based on Information of Microstructure
