位错偏析诱导镁合金纳米化及其变形机制研究

Grain refinement can improve both the strength and ductility of magnesium (Mg) alloys, which is of great significance for its application in the lightweight components. The development of new methods to help the nanocrystallizaiton of Mg alloys becomes a hotspot of the current research. However, the grain refinement induced by dynamic recrystallization, which needs to deform the material to a large strain, is not suitable for Mg alloys owing to their poor formability at low temperatures. Meanwhile, high speed of recover occurred when the Mg alloys are deformed at high temperature, which also restrains the grain refinement. In this project, we propose a novel method to produce nanocrystalline Mg alloys, which is assisted by dislocation segregations. The detailed research plans include: To explore the preparation technology, and to optimized the process of nanocrystalline Mg alloys; To investigate the relationship between microstructure evolution and mechanical properties enhancement, and to explore the processing of nanocrystallization; To study deformation mechanism of nanocrystalline Mg alloys using in-situ atomic-scale microscopy. There are two key scientific issues to be addressed in this project including: The structure, properties and the formation mechanism of nanocrystalline Mg alloy, and in situ study the deformation mechanism of the nanocrystalline Mg alloys. The research of this project will enrich the technology of nanocrystallization of magnesium alloys and promote the industrial application of Mg alloy with high strength and ductility.

晶粒细化可同时提高镁合金的强度与塑性，对其在轻量化领域的推广应用具有重要意义。如何以新思路，解决镁合金纳米化困难的问题，开发其新型的纳米化技术是目前的研究热点之一。由于传统的动态再结晶细化晶粒需要对材料施以大变形量，并且为了抑制回复，变形温度还不能太高，该机制并不适用于变形能力差的镁合金，本项目拟利用溶质元素与位错的交互作用，以位错偏析诱导镁合金的纳米晶形成，提出一种新型的适合于镁合金的晶粒纳米化机制。具体研究内容包括：探索纳米晶镁合金的制备技术及其工艺优化；研究纳米晶镁合金的组织演化与力学性能的关系，探索其纳米化过程；基于原位变形技术对纳米晶镁合金的纳米和原子尺度变形机制进行深入研究。拟解决的两个关键科学问题是：纳米晶镁合金的结构、性质及形成机理和纳米晶镁合金的原位变形机制。该项目研究及其成果对于丰富镁合金纳米化研究技术，推动高强韧镁合金材料的工业化应用具有重要意义。

晶粒细化可同时提高镁合金的强度与塑性，对其在轻量化领域的推广应用具有重要意义。如何以新思路，解决镁合金纳米化困难的问题，开发其新型的纳米化技术是目前的研究热点之一。本项目通过冷轧变形结合热处理工艺成功制备了Mg-Ag纳米晶材料。研究发现，高密度非基面位错在轧制变形过程中产生并缠结形成位错墙和位错胞；在后续退火过程中Ag元素在位错核心通道形成偏析结构，与位错发生交互作用，发生回复诱导镁合金位错墙转变为小角晶界促使纳米晶的形成。此外，基于纳米异构材料的理念，本项目制备了Mg-5Y/Mg-11Y/Mg-5Y和AZ31/GW103K/AZ31层状异构镁合金材料，获得了高强高韧的综合力学性能。. 本项目还深入研究了合金元素，晶粒尺寸对镁合金变形机制的影响。通过纯Mg和Mg-Y合金对比研究发现，仅3%的Y元素的添加使得Mg-Y合金的延伸率从5.3%提升到20.7%。TEM结果表明大量的非基面<c>位错和层错是Mg-Y合金获得高延伸率的重要原因。而不同晶粒尺寸的纯Mg的研究表明，晶粒尺寸为125μm的纯Mg由于主要产生基面<a>滑移，其塑性较差。双束条件表明随着晶粒尺寸减小到5.5μm时，大量层错和非基面<c+a>位错的产生是细晶纯Mg的额外变形机制，使纯Mg拥有较好的加工硬化能力和良好的均匀延伸率，带来材料强度和塑性的同时提高。. 该项目研究及其成果对于丰富镁合金纳米化研究技术，推动高强韧镁合金材料的制备及工业化应用具有重要意义。