Molecular Dynamics Simulation Of The Interaction Of Defects And Twinning In Magnesium Single Crystal

ABSTRACT:Magnesium and its alloys are considered to be the most potential for development and application of "green materials" in the21st century due to their low density and relatively high specific strength. However, the application of magnesium alloys is restricted due to the limited forming capacity and the poor corrosion resistance. From the mechanical point of view, magnesium and its wrought alloys show a pronounced direction-dependence of plastic yielding and work hardening. This feature is due to the crystal structure of magnesium, which is a hexagonally close-packed structure. Compared to face-centered cubic or body-centered cubic metals, the number of slip systems allowing plastic deformation in magnesium is limited. Deformation mechanisms acting on magnesium and its alloys are sophisticated and still a subject to be discussed. Therefore, the deformation mechanism is the key rule of magnesium and its alloys in recent years.In this thesis, molecular dynamics simulation is applied to investigate deformation mechanism in magnesium single crystal, and the relationship between different defects in magnesium single crystal and twinning is discussed. Four types of defects are selected, including the point defect, the <1010> line defect, the <1210> line defect and the planar defect. The influence of different defects on the movement of the {1012} twin at different temperatures, loading rates and boundary conditions are considered. The results show that:the main plastic mechanisms of the crystal under shear are stacking faults and phase transitions. Different defects make different effects on {1012} twins movement. The point defect and the linear defects have no distinctly influence on the movement of twin. For the planar defect, at ultralow temperature (5K), it will impede twins movement. However, as the temperature increases, the effect of this planar defect hindering the twin boundaries movement can be ignored. Moreover, it is found that the loading rate have no distinct influence on the interaction between defects and twins, but it will affect the mechanism of plastic deformation of the single crystal.