镁合金晶间变形协调性定量研究及高塑韧性镁合金设计

The application of wrought magnesium alloys is restricted due to their poor ductility and workability at room temperature caused by the plastic anisotropy and the poor deformaiton compatibility at grain level. This project investigates deformaiton compatibility quantitatively by using in-situ deformation in scanning electron microscopy (SEM) combined with electron backscattered diffraction (EBSD), focused ion beam miller (FIB) and digital image correlation (DIC) techniques. In addition, this project develops Crystal Plasticity Based Finite Element Method ( CPFEM) modeling by considering grain orientations and grain morphology. Current discussion on deformaiton mechanism of Mg alloy are limited on that in grain interior or on macro-scale, few comments were provided on the intergranular deformation behavior, here the project will make the breakthrough based on the investigate quantitatively and CPFEM modeling. The reliability on the microstructure of deformaiton behavior in macro-, intergranular or intragranular will be discussed further. And based on the datas from in-situ observation, the effects of grain orientations, distribution and grain boundaries on the crack nucleation and propagation were analyzed as well. The goal of the project is to get the key microstructure factors which affect the deformation compatibility, to suggest a good way to improve the deformation compatibiliy of Mg alloy, and to develop a reliable CPFEM models relating to the grain orientations, grain morphology and grain boundaries. Finally give strong supports for developing of high ductility wrough Mg alloy.

镁合金从介观到宏观尺度存在变形行为各向异性，晶间变形协调性差，导致镁合金的成形性及断裂韧性差，这是限制其工业应用的瓶颈问题。本项目拟采用原位背散射电子衍射（EBSD）、原位扫描电子显微镜（SEM）、辅助聚焦离子束（FIB）及数字图像相关（DIC）技术，对镁合金晶间变形协调性定量分析。采用晶体塑形有限元法，引入晶粒取向及形貌相关的材料因子，优化镁合金多晶体塑性有限元模型。突破现有镁合金变形理论从晶内直接跨度到宏观的局限，讨论晶内、晶间变形及宏观应力应变响应对镁合金微观组织的依赖性。从晶间变形的原位观察及分析出发，揭示晶粒取向、分布及界面特征对镁合金裂纹萌生及扩展的影响规律。探明影响镁合金晶间变形协调性的关键微观组织因素，并提出改善晶间变形协调性的微观组织调控原则，建立考虑晶粒取向、晶粒形貌及界面因素的镁合金多晶体塑性变形模型。为开发高塑韧性、高成形性镁合金奠定理论基基础。

镁合金从介观到宏观尺度存在变形行为各向异性，晶间变形协调性差，导致镁合金的成形性及断裂韧性差，这是限制其工业应用的瓶颈问题。为了探明晶粒度、织构、晶间、相界等多维结构对镁合金介观及宏观变形行为的影响，并探索高塑韧性合金的设计理论。本项目采用了原位背散射电子衍射(EBSD )、原位扫描电子显微镜(SEM)、辅助聚焦离子束(FIB)及数字图像相关(DIC)技术，对镁合金晶间变形协调性定量分析。介观尺度的量化分析，有助于突破现有镁合金变形理论从晶内直接跨度到宏观的局限，讨论晶内、晶间变形及宏观应力应变响应对镁合金微观组织的依赖性。从晶间变形的原位观察及分析出发，揭示晶粒取向、分布及界面特征、第二相的分布及相界面构型等对镁合金裂纹萌生及扩展的影响规律。本项目取得了如下成果：.（1）建立了织构组分、晶粒度、晶粒分布界面对应的宏观应力应变相关性。探明了晶粒度、织构与室温力学性能量化关系。.（2）基于原位 SEM、EBSD 及 DIC 的数据定量分析了镁合金晶内变形模式及晶间变形模式的传递。提出了考虑晶粒取向和界面关系的变形协调因子Mk，建立了Mk与力学行为的量化关系。.（3) 通过结合分析裂纹附近的微观组织形貌和晶粒取向信息相关性，表明裂纹的产生与晶间的变形不协调性有着明显的关系。可采用F1因子来定量分析镁合金的裂纹萌生问题，并且还探明了Mg-8%Gd-3%Y 合金中第二相分布、织构、晶粒度等因素对裂纹萌生及扩展的影响。提出了提高镁合金断裂韧性的微观组织调控原则。.（4)在探明了单相合金晶粒取向、晶界特征对镁多晶体局部应变分布及变形不均匀性的影响机理的基础上。针对Mg-Li双相合金的介观尺度变形行为进行了研究，探明了双相界面及构型对局部应变及变形行为的影响机理，提出了改善镁合金晶间变形协调性的微观组织调控原则。.（5）本项目通过TEM与原子分辨率的HAADF-STEM表征技术，对挤压态Mg-0.5Ce和Mg-2Gd合金在200℃下的蠕变性能及蠕变机理进行深入的研究发现，稀土原子除了与位错发生弹性交互作用带来固溶强化以外，还可以在位错附近偏聚，钉扎位错，从而改善镁合金的高温抗蠕变性能。