The Twinning Characteristics And Plastic Deformation Mechanism In Extruded AZ31 Magnesium Alloys

This work mainly aims to investigate the twinning behavior and variant selection mechanism of an extruded AZ31 magnesium alloy during uniaxial compression and rolling at room temperature. Different deformation structures were obtained through uniaxial compression and rolling, and then were characterized by using electron backscatter diffraction(EBSD). In order to understand in depth the mechanism of plastic deformation, the variant selection of twins or paired twins in different deformation geometries were analyzed by crystallography calculation and analysis.The plastic deformation mechanism was discussed by analyzing the microstructure characteristics such as misorientation angle of grain boundaries(GBs) and twin area fraction after deformation. The conclusions were as follows:(1) lots of {10-12} extension twinning were activated in most grains and paired twins were formed at the GBs during the process of compression along ED(extruding direction); The misorientation angle was mainly concentrated near 86?, but the proportion of misorientation angle between 2?-5? was small. Meanwhile, the area fraction of {10-12} extension twins increased with the deformation, showing that the main deformation mechanism is twinning. However, the area fraction of {10-12} extension twins decreased when samples were compressed perpendicular to ED. Then the proportion of misorientation angle between 2?-5? became larger, indicating that slip deformation played an important role during the increasing deformation that samples were compressed perpendicular to ED.(2) The area fraction of twins or paired twins was the largest among all the rolled samples when ED is parallel to ND(normal direction), which was related to the orientation of grains. The percentage of misorientation angle between 2?-5? in rolled samples became lower than that of the uniaxially compressed samples. This is because that slip deformation couldn’t be activated at a high strain rate, but the formation of twins and paired twins can relieve the local stress concentration.The variant selection mechanism was analyzed, and the results show that:(1) Most of paired twins in the samples either compressed uniaxially or rolled in different directions had relatively high Schmid factor(SF), and more than 70% of the active twin variants had the first or second SF Rank, confirming that the variant selection of twins generally obey the Schmid Law.(2) Over half of paired twins in uniaxial compressed samples had the first m? Rank, and more than 70% of paired twins had the first m? Rank in the rolled samples. This implied that the strain coordination played an important role in variant selection of paired twins.(3) Paired twins with simultaneously high SF and high m? prefer to form at low angle grain boundaries and can coordinate macro-deformation better in extruded Mg alloys.