基于溶质拖曳的镁稀土合金织构及晶界设计理论研究

Precipitates in Mg alloy are effective strengthening agents by restricting dislocation motion, however, the ductility could be decreased due to the obstacles effects. Texture randomization and grain boundaries strengthening are two desirable approaches to obtain compensatory ductility of Mg alloys due to the solute drag effect. It is important to understand the mechanism of texture-random to develop Mg alloy with random texture, and it is possible to design "strong" grain boundaries because solute drag effect will lead to decrease in grain boundaries mobility. In the project, the effect of Gd solute segregation on basal <a>, non-basal <c+a> dislocation slip, (10-12) extension, (10-11) contraction twinning and grain boundaries mobility will be studied by High Angle Annular Dark Field (HAADF), Electron Backscatter Differection (EBSD) and In-Grain Misorentaion Axes (IGMA) etc. The results are helpful to understand the mechanism of texture randomization for Mg-RE alloy. In another way, the Hall-Petch relationship in Mg and Mg-1%Gd alloy will be investigated, and quantitative analysis on grain boundaries slides will be studied by Atomic force microscopy (AFM) , Electron Probe Micro-analyzer (EPMA) and mechanical properties testing. Based on the experiment results and the phase-field simulation of grain boundaries mobility related to solute drag effect, a new theory and method for design "strengthening" grain boundaries could be obtained.

虽然有效的析出相能够增强镁合金，但是析出相增强的同时，合金塑韧性往往降低。弱化镁合金织构及增强晶界阻碍位错的能力（"强"晶界设计）是有效弥补塑韧性损失的科学路径。镁稀土合金中的溶质拖曳效应为织构弱化及晶界增强提供了可能。本项目设计了Mg-Gd二元合金体系（Gd含量0-7wt.%）,采用高角环形暗场扫描透射电子显微术（HAADF）、电子背散射衍射技术(EBSD)及晶内位向轴差法（IGMA）等方法研究Gd元素偏聚对镁合金中基面<a>滑移、非基面<c+a>滑移、拉伸/压缩孪生机制、以及晶界可动性的影响，建立基于溶质拖曳的镁稀土合金织构弱化机理。设计不同晶粒度的镁及Mg-1%wt.Gd合金，研究合金强度与晶粒度相关性，并采用原子力显微镜（AFM）及原子探针（EPMA）等方法定量分析晶界滑动对总变形量的贡献，结合晶界滑动与溶质原子交互作用的相场模拟，建立基于溶质拖曳的"强"晶界设计理理论。

虽然有效的析出相能够增强镁合金，但是析出相增强的同时，合金塑韧性往往降低。弱化镁合金织构及增强晶界阻碍位错的能力（“强”晶界设计）是有效弥补塑韧性损失的科学路径。镁稀土合金中的溶质拖曳效应为织构弱化及晶界增强提供了可能。本项目设计了Mg-Gd 二元合金体系（Gd 含量0-7wt.%）,采用高角环形暗场扫描透射电子显微术（HAADF）、电子背散射衍射技术(EBSD)结合粘塑性自洽模型（VPSC）模拟的方法研究Gd 元素偏聚对镁合金中基面<a>滑移、非基面<c+a>滑移、拉伸/压缩孪生机制、以及对织构演变的影响，建立了基于溶质拖曳的镁稀土合金织构弱化机理。研究Mg-Gd合金力学性能与晶粒度、织构的相关性，并采用原位EBSD及数值图像相关技术（DIC）等方法定量分析镁合金介观尺度变形行为，提出了强韧性镁合金设计理理论。