中文摘要：

实验表明镁合金在制造过程中不可避免的会出现缩孔和微裂纹两种微观缺陷，这两种微观缺陷对镁合金的力学性能有着重要影响．通过分子动力学方法在原子尺度下分别对带有缩孔和微裂纹镁合金的塑性变形过程进行了研究，原子间的相互作用由改进嵌入原子势来描述，观察到了hcp结构金属裂纹扩展及失效过程．计算结果表明：镁合金的裂纹扩展是一个复杂的过程，带缩孔型钝裂纹顶端镁合金的塑性变形和破坏机制为：裂尖钝化和沿hcp晶体结构滑移系的位错发射；带尖裂纹顶端镁合金的塑性变形和破坏机制为：主裂纹附近产生大量的副裂纹，副裂纹快速长大并最终与主裂纹联结，同时伴有沿滑移系的位错发射．

英文摘要：

Experiments show that there will be two types of micro-defects in the manufacturing process of magnesium alloys, including the shrinkage cavity and micro crack, which effect on the mechanical properties of magnesium alloys significantly. In this study, the plastic deformation processes of magnesium alloys around crack tips at atomic scale level are examined through molecular dynamics （ME）） simulation. The Modified Embedded Atom Method （MEAM） potential is employed to characterize the interatomic interactions of magnesium alloy specimen with a shrinkage cavity and a sharp crack. The crack propagation and failure processes for hexagonal close-packed （hcp） structure ave observed around the crack tips. The calculation results reveal that the crack propagation of magnesium alloy is quite complex process. The plastic deformation and failure mechanism of shrinkage cavity are the crack blunting and dislocation emission along the slip systems of hcp crystal structure. The plastic deformation and failure mechanism of sharp crack are a great deal of side cracks formed around the main crack, the side cracks grow rapidly and eventually link up with the main crack, as well as the dislocation emission along the slip systems.