Mg-Sn-Zn合金中沉淀析出反应及其强化相非均匀形核机理研究

The Mg-Sn system is a precipitation-hardened magnesium alloy, and the precipitation hardening can be significantly enhanced by a minor addition of Zn.The additon of Zn makes Mg2Sn precipitates finer and manipulates their shape. However, the reason that various orientation relationships coexist between precipitate and matrix, the mechanism of Zn manipulating the shape of precipitates, and the nucleation and growth mechanism of precipitates are not still thoroughly understood. In this project, the advanced analysis methods such as HAADF and 3D tomography are used to investigate the microstructure of Mg-Sn-Zn alloy. The crystallographic nature of the coexistence of a variety of orientation relationship between the precipitates and the matrix can be clear by the accurate determination of the structure of precipitates and the orientation relationship. The mechanism of Zn manipulating the morphology of precipitates, and the nucleation and growth mechanism of precipitates can be revealed via the quantitative characterization of the structures of precipitates and interface in the specimen with different aging time at atomic scale. This project will enrich the theory of manipulating precipitate shape in magnesium alloys, and provide a foundation on the design of high performance magnesium alloys by microalloying.

Mg-Sn合金是析出强化镁合金体系，研究表明添加Zn可以显著增强其析出强化效果。添加Zn可以细化Mg2Sn析出，并改变Mg2Sn的形状。然而，对于Mg-Sn-Zn合金中析出相与Mg基体存在多种取向关系的原因、添加Zn改变析出相形状的机理以及析出相的形核长大机理还缺乏充分的认识。本项目以Mg-Sn-Zn合金为研究对象，利用HAADF和三维重构等先进的微观结构表征手段，通过对析出相结构、形貌和取向关系的准确确定，揭示Mg-Sn-Zn合金中同时存在多种析出相形貌和取向关系的晶体学本质；通过对不同时效阶段析出相以及析出相/基体界面结构原子尺度的定量表征，阐明Zn改变析出相形貌的机理以及析出相的形核长大机理。本项目研究结果可以丰富镁合金中的析出相形貌调控理论，为通过微合金化提高镁合金的性能及开发新合金提供理论依据。

研究发现，在Mg-Sn-(Zn)合金的时效早期中会形成高密度、尺寸3nm左右的原子团簇，并且电子束辐照会诱导原子团簇的产生和长大。在Mg-Sn-Zn合金中观察到与基体保持五种取向关系的Mg2Sn析出相，其中有三种取向关系为首次报道。在不同形貌和取向关系的Mg2Sn析出相与基体界面都观察到了Zn元素的偏聚。开发了一种Mg-Al-Sn-Zn高强变形镁合金，经过T6处理后，该合金的屈服强度达到341MPa，抗拉强度达到409MPa，延伸率4.0%。