Mg-Sn-Zn合金预变形缺陷作用下的沉淀相特征及相变机制研究

轻质高强镁合金是金属结构材料领域的研究热点，调控沉淀相特征提高其强化效果是发展高强镁合金的重要思路。Mg-Sn-Zn合金是一种极具发展潜力的低成本可时效强化镁合金，研究表明，预变形可细化该合金的沉淀相，改变其形貌，提高其强化能力。然而，预变形引入的位错、孪晶界、层错对沉淀相形貌、尺寸、分布、取向关系、惯习面等特征的影响及相关的相变机制尚不明确。本项目采用多维多尺度表征、原子尺度图像定量分析、结合力学性能测试，研究Mg-Sn-Zn合金中：不同预变形缺陷作用下沉淀相上述特征的变化，阐明不同缺陷对沉淀相特征的定量影响；沉淀相在不同预变形缺陷上析出时结构和成分的演变规律及其与缺陷应变的相互作用，揭示不同缺陷上的析出相变机制；预变形缺陷作用下沉淀相引起的力学性能变化及其与位错滑移、孪生的交互作用，评价缺陷调控沉淀相的强化效果。研究成果可为利用缺陷调控镁合金中沉淀相特征，进而调控合金力学性能提供指导。

Lightweight and high strength magnesium alloys are the hot topic in the field of metallic structural materials. Regulating precipitate features to improve their strengthening effects is a significant method to develop high strength age-hardenable magnesium alloys. Mg-Sn-Zn alloy is a low-cost age-hardenable alloy with a great developing potential. It has been reported that pre-deformation can refine precipitates, change their morphologies and improve their strengthening effect in the alloy. However, it remains unclear that how the dislocation, twin boundary, and stacking fault introduced by pre-deformation effect the morphology, size, distribution, orientation, habit plane of the precipitate, and what the phase transformation mechanism is. This project takes the Mg-Sn-Zn alloy as the research object, utilizing multi-dimensional and multi-scale accurate characterization, quantitative analysis of atomic-scale image and mechanical property test to study the following things. First, the effect of different pre-deformation defects on the precipitate features in the alloy would be investigated carefully to clarify the quantitative effect of the different defects on the precipitate features. Then, structure and composition evolution of the precipitate on the different pre-deformation defects and the interaction of strain between precipitate and different defects would be studied to reveal the phase transformation mechanisms on these defects. Finally, the change of mechanical property of the alloy caused by the precipitate precipitation on the pre-deformation defects and the interaction between the precipitate and dislocation gliding and twinning during plastic deformation would be investigated to evaluate the strengthening effect of these precipitates. The research outcomes of this project can guide the precipitate feature modification via introducing defects and then provide a scientific guidance to improve the mechanical property of magnesium alloys.