轻金属镁及镁合金中<c+a>位错的行为及其对塑性的影响

Magnesium and magnesium alloys are of great potential for weight reduction and fuel efficiency in aviation, aerospace and automotive industries. One of the main problems limiting the wide applications of these lightweight materials is their low ductility. This is caused by the dearth of slip systems activated to accommodate plastic deformation, originating from the low symmetry and high anisotropy of the hexagonal close-packed (HCP) lattice structure. It is well known that pyramidal <c+a> slip is a requisite for accommodation of plastic deformation, yet it is also the most difficult slip mode in HCP metals. Therefore, enhancement of pyramidal <c+a> slip activities becomes the key for improving the ductility of HCP metals. In the present study, the nucleation, dissociation, core structure and stress required for slip of Pyramidal II <c+a> dislocations are systematically investigated, via combination of first principles calculations and molecular dynamics simulations, to reveal how pyramidal <c+a> slip influences the ductility of HCP Mg. Furthermore, effects of alloying and microstructure/defects on the nucleation and slip behavior of pyramidal <c+a> dislocations are also investigated. Favorable alloying additions and microstructure/defects that enhance pyramidal <c+a> dislocation nucleation and slip will be suggested to guide the design of high-ductility magnesium and magnesium alloys.

轻金属镁及镁合金在航空、航天和汽车工业的结构减重和降低油耗方面潜力巨大。而目前限制镁及镁合金广泛应用的主要问题之一是其较差的塑性变形能力。密排六方（HCP）晶体结构的对称性低而各向异性程度高，导致塑性变形中能启动的用以协调变形的滑移系数量严重不足，这是影响其塑性的主要原因。HCP晶体的锥面<c+a>滑移是协调变形所必需的模式，同时也是最难启动的模式，因而对锥面<c+a>滑移行为的调控成为HCP金属塑性调控的关键。本研究采取第一性原理计算结合分子动力学模拟，对镁中II型锥面<c+a>位错的形核、位错分解与平衡构型、滑移所需应力等展开系统的研究，从微观上揭示锥面<c+a>滑移如何影响HCP金属的塑性变形能力。在此基础上，系统研究合金化和微结构对II型锥面<c+a>位错的形核和滑移行为的影响，寻找有利于锥面<c+a>位错形核和滑移的合金元素和微结构类型，为提高HCP镁的塑性变形能力提供设计思路。

轻金属镁及镁合金在航空、航天和汽车工业的结构减重和降低油耗方面潜力巨大，而其有限的塑性变形能力是制约其广泛应用的主要问题之一。本研究针对密排六方（HCP）晶体结构能启动的用以协调变形的滑移系数量严重不足的问题，采用大规模原子模拟方法系统研究了协调HCP晶体变形所必需同时也是最难启动的锥面<c+a>位错的滑移行为，包括镁中锥面<c+a>位错的自然形核、位错分解与平衡构型，I型和II型锥面上四种不同性质的<c+a>位错滑移所需的应力及滑移行为，螺位错的交滑移行为及位错惯性等。结果显示了<c+a>位错行为的极高的各向异性及复杂性。而螺位错存在在不同滑移面间（包括一个新发现的滑移｛-12-11｝）活跃地交滑移的行为，为通过促进交滑移来改善塑性提供了一种新的简单的途径。这些发现拓宽了我们对HCP金属塑性变形基础物理的认识，为提高HCP镁的塑性变形能力提供了理论基础和现实途径。