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冲击波诱发含孔Mg-3Al-1Zn合金位错形核及演化行为研究

SHOCK-INDUCED DISLOCATION NUCLEATION AND EVOLUTION IN Mg-3Al-1Zn ALLOY WITH INITIAL VOID

  • 摘要: 由于汽车和航空航天领域对轻量化材料的需求, 镁及其合金因其具有低密度、高强度等一系列优点而拥有难以替代的地位. 目前, Mg-3Al-1Zn合金是目前应用最广泛的一种商用镁合金, 研究其在冲击载荷作用下的变形机理和冲击响应, 对促进镁合金在汽车和航空航天领域的应用具有重要意义. 本文针对 \text0001 \text10\bar \text1 \text0两种不同冲击晶向, 采用分子动力学方法讨论了含有圆柱形孔洞的Mg-3Al-1Zn合金模型在冲击波作用下孔洞表面位错形核与演化的过程. 研究表明, 孔洞附近滑移系的激活强烈依赖于冲击晶向, 当沿着 \text0001 晶向冲击时, 基面位错在孔洞表面优先形核, 随后沿着与之前21°的夹角方向滑移形成一个大角度晶界; 对于\text10\bar \text1 \text0晶向的冲击, 孔洞附近的变形最初由柱面位错主导, 随后大量的基面位错分布在孔洞周围. 基于应力波理论进一步讨论了冲击波前沿导致的孔洞附近晶格转向行为, 发现孔洞表面的反射等容波(SV2)决定了孔洞表面位错的形核位置和滑移方向, 而反射无旋波(P2)决定了孔洞附近与坍缩有关的塑性变形行为. 最后, 结合孔洞周围应力场分布分析了两种冲击晶向下孔洞表面位错的分布规律. 总的来说, 本文的分子动力学模拟结果与基于应力波理论的分析、孔洞周围应力场的分析均吻合较好, 获得了孔洞附近的位错形核及演化规律.

     

    Abstract: Due to the demand for lightweight materials in automotive and aerospace fields, magnesium and its alloys play an irreplaceable role due to a series of advantages such as low density and high strength. Currently, Mg-3Al-1Zn alloy is one of the most widely used commercial magnesium alloy. It is of great significance to study its deformation mechanism and shock response of Mg-3Al-1Zn alloy. In this paper, molecular dynamics method has been used to study the shock behaviors of Mg-3Al-1Zn alloy with a cylindrical void. For 0001 and \text10\bar \text1 \text0oriented Mg-3Al-1Zn specimen, the nucleation and evolution of dislocations near void surface induced by shock wave are discussed. Simulation results show that the activation of slip system near the void is strongly dependent on the shock orientation. In 0001 orientation, basal dislocations preferentially nucleate near the void, and basal lattices near void are found to be rotated by ~ 21° and finally form a high-angle grain boundary. However, prismatic dislocations are observed to be the preferentially mode along the \text10\bar \text1 \text0 orientation, subsequently, a large number of basal dislocations nucleated. Based on the theory of stress wave, it is found that the dislocation behaviors near the void are greatly affected by the reflected isometric wave (SV2), while the plastic deformation behaviors associated with void collapse are greatly affected by the irrotational wave (P2). Moreover, the distributions of the shear stress near the void are analyzed to predict the distributions of the nucleated dislocation under different shock orientations. In general, simulation results in this paper are in good agreement with the prediction based on stress wave theory and the distributions of the resolved shear stress, and the nucleation and evolution mechanisms of the dislocations near the void are obtained.

     

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