Strain-Path Dependence of {10(1)over-bar2} Twinning in a Rolled Mg-3Al-1Zn Alloy: Influence of Twinning Model

In magnesium and its alloys, {10 (1) over bar2} tension twinning is an important deformation mode and is highly dependent on the strain path. Although the {1012}-twinning behavior has been extensively modeled, the effects of twinning models on the predicted results has seldom been compared. In this study, two typical twinning models, predominant twin reorientation (PTR) and twinning-detwinning (TDT), were chosen to simulate the {10 (1) over bar2}twinning-predominant deformations of a Mg alloy AZ31 rolled plate, in compression along the transverse direction (TD-c) and in tension along the normal direction (ND-t), and the results were compared with experimental data. In addition to the strain-stress curves in the ND-t and TD-c, six other flow curves were used to determine the material-parameter inputs for the simulations with the elastic visco-plastic self-consistent (EVPSC) model. Compared with the PTR model, the TDT model permits better curve fitting and texture prediction. The PTR model cannot fit the TD-c and ND-t flow stresses simultaneously, whereas the TDT model can. The best-fit parameters for the two models are identical at low strains but diverge somewhat at high strains. The simulated twin volume fractions are similar in the two models, but the predicted textures are significantly different. The PTR model can only reproduce the texture at strains over 5 pct in the TD-c and cannot reproduce the deformed texture in the ND-t. In contrast, the TDT model can reproduce all the experimental textures. To fit both the compression and tension curves well, strong latent hardening of the critical resolved shear stress (CRSS) for {10 (1) over bar2} twinning by other twinning systems (h(tt)) is necessary. The h(tt) favors the twin variant with the highest Schmid factor in compression. The h(tt) increases the CRSS for all {10 (1) over bar2} twinning systems in tension, but the CRSS for the dominant twinning system remains relatively low in compression.