纯镁及镁合金的微塑性变形行为研究

With the increasing application of Mg alloys, the microplastic deformation of Mg alloys has drawn the attention of researchers, because the microplastic deformation is closely connected with the damping behavior, fatigue and other properties of materials. The first step of the project is to investigate the effect of grain size and texture on the microplastic deformation behavior of pure Mg, then the effect of alloying and second phases on the microplastic deformation behavior of Mg alloys is studied. The microstructure of the Mg and its alloys after loaded at different microstrains will be observed by transmission election microscope (TEM), and an in situ transmission electron microscopy study will be performed on the Mg and Mg alloys during cyclic loading and unloading in the microyield regime. In addition, the lattice dependant strain development in the elastic as well as in the plastic region during the cyclic loading and unloading of the Mg and Mg alloys in the microyield regime will be investigated. The microplastic deformation behavior and microstructure evolution will be studied systematically through careful analysis of the relation between cyclic loading-unloading and microstructural evolution, in order to shed light on the mechanism of microplastic deformation of Mg and Mg alloys. The project will promote further understanding of the damping behavior and fatigue of magnesium alloys, and provide theoretical guidance for developing high performance magnesium alloys with high damping capacity, high dimensional stability and high fatigue resistance.

随镁合金应用的增加，与镁合金构件在服役条件下的阻尼性能和疲劳性能等密切相关的镁合金微塑变研究逐渐引起了研究者的关注。本项目将首先以商业纯镁为主，采用单向拉伸试验和循环单向加卸载试验研究晶粒度和织构对纯镁微塑变的影响规律，然后研究合金化和第二相对镁合金微塑变行为的影响。通过透射电子显微镜研究不同微小塑性变形量下显微组织、原位TEM观察微塑变加载卸载下的动态组织演变规律，辅以同步辐射原位加载获得的晶格应变演化。将循环加卸载的应力-应变测试与微观组织结构的观察结合起来，系统深入地研究镁合金微塑性变形的变形规律及显微组织结构演变，揭示微塑变机理。研究结果将加深对镁合金阻尼行为和疲劳行为的理解，为高阻尼镁合金、尺寸稳定性镁合金、耐疲劳镁合金的研究开发提供理论指导。

随镁合金应用的增加，与镁合金构件在服役条件下的阻尼性能和疲劳性能等密切相关的镁合金微塑变研究逐渐引起了研究者的关注。本项目采用高应变测试精度单向拉伸法和循环拉伸加载卸载法研究预晶粒度、织构、合金化、第二相对纯镁和镁合金微塑变行为；研究了微塑性变形过程中的组织演变规律；研究了纯镁及镁合金的阻尼和微塑变的内在联系，揭示了纯镁和镁合金微塑变的微观机理。.纯镁的微塑变包括两个阶段：第一阶段对应塑性应变小于2×10–4的区域，Schmid因子较大晶粒内部位错从钉扎点上脱钉并在基面滑移，可动性较大，激活体积较大，加工硬化指数较小；当塑性应变高于2×10–4时，由于位错在同一滑移面上运动而发生缠结和堆积，可动位错密度降低，材料硬化，所以具有较大的加工硬化指数和较小的位错滑移激活体积，这时微塑变进入第二阶段。纯镁微塑变行为和与塑性变形相关的阻尼可用同样的位错机制来解释，它们有着相同的物理本质。.晶粒度和织构显著影响纯镁的微塑变行为。随着晶粒尺寸的增大，纯镁的微屈服应力降低，内耗和滞弹性应变增加。不论织构如何，微塑性变形只与基滑移有关，即使在拉伸孪生有利的取向，微塑性变形阶段的变形机理仍为基滑移，而非拉伸孪晶，即纯镁的微塑变主要是由基面上的<a>位错滑移来协调，这是微塑变和宏观塑变机理的主要区别。.不同合金元素对镁的微塑变行为有显著影响。高固溶度的Mg-1Al中位错受到大量固溶Al原子的钉扎，极大的降低位错线上弱钉扎点间距，提高镁合金在较小应变下的正切弹性模量，摩擦应力和背应力；而固溶度低的Mg-1Si中只有少量的溶质原子作为位错的弱钉扎点，导致铸态Mg-1Al合金的微屈服强度较高。.含LPSO相Mg-Gd-Y-Zn-Zr合金的微屈服强度高于不含LPSO的合金。峰时效态Mg-9Gd-3Y-2Zn-0.4Zr-0.2Ca挤压态合金析出大量弥散析出纳米第二相，显著阻碍位错滑移，导致残余塑性应变显著降低，微屈服强度达到280MPa，显著高于高强2024铝合金及其它镁合金，在要求高尺寸稳定性的轻质构件中有显著的应用前景。