To investigate the role of pre-twins in Mg alloy sheets during warm planar deformation, the stretch forming is conducted at 200 °C. Results suggest the formability of the pre-twinned AZ31 Mg alloy sheet is enhanced to 11.30 mm. The mechanisms for the improved formability and the deformation behaviors during the planar stretch forming are systematically investigated based on the planar stress states. The Schmid factor for deformation mechanisms are calculated, the results reveal that planar stress states extremely affect the Schmid factor for {10-12} twinning. The detwinning is activated and the prismatic slip is enhanced in the pre-twinned sheet, especially under the planar extension stress state in the outer region. Consequently, the thickness-direction strain is accommodated better. The dynamic recrystallization (DRX) type is continuous DRX (CDRX) regardless of the planar stress state. However, the CDRX degree is greater under the planar extension stress state. Some twin lattices deviate from the perfect {10-12} twinning relation due to the planar compression stress state and the CDRX. The basal texture is weakened when the planar stress state tends to change the texture components.

为了研究镁合金板在温平面变形过程中预孪晶的作用，在 200 °C 下进行拉伸成形。结果表明，预孪晶 AZ31 镁合金板的成形性提高至 11.30 mm。基于平面应力状态，系统地研究了平面拉伸成形过程中改善成形性和变形行为的机制。计算了变形机制的Schmid因子，结果表明平面应力状态极大地影响了{10-12}孪晶的Schmid因子。预孪晶片材中的解孪被激活，棱柱滑移得到增强，特别是在外部区域的平面拉伸应力状态下。因此，更好地适应厚度方向应变。动态再结晶（DRX）类型是连续DRX（CDRX），与平面应力状态无关。然而，平面拉伸应力状态下CDRX程度更大。由于平面压缩应力状态和 CDRX，一些孪晶晶格偏离了完美的 {10-12} 孪晶关系。当平面应力状态倾向于改变织构成分时，基底织构就会减弱。