多元析出强化Mg-Sn-Mn-Ag(-Zn)合金中多析出交互作用的实验和理论研究

多元合金中，作为影响合金沉淀强化效果的两个重要因素，沉淀相的形核密度和晶体学形貌都直接或间接受非均匀形核行为的影响。现有沉淀强化镁合金的开发尚处于试错法阶段，一个重要原因在于对沉淀相非均匀形核的规律及其对共沉淀相晶体学形貌的影响机制尚不清楚。本项目拟利用透射电镜，研究Mg-Sn-Mn-Ag(-Zn)多元合金时效过程中的组织演化，精确测定不同时效阶段形成析出物（含元素团簇）的种类、分布，重点关注两个或多个相互依存析出物的析出规律，并获得沉淀相完整、系统的晶体学数据；理论方面，运用晶体学模型并结合析出动力学、热力学因素，对共沉淀相、基体相互间的界面匹配结构及缺陷进行分析，进而阐明共沉淀相晶体学与多析出物异质形核的交互作用机制，提出在析出型相变中以晶体学匹配为原则诱导沉淀相异质形核的组织设计思路。本项目研究结果有助于推进对多析出相析出交互作用规律的认识，并为镁合金沉淀相组织设计提供理论指导。

The nucleation density and crystallographic morphology of precipitates are two dominating factors affecting the age-hardening response of precipitation-hardening alloys. In multi-component alloys, both of these microstructure features are dominated or affected by the heterogeneous nucleation behaviors. However, alloy development with the purpose of enhancing age-hardening response in Mg alloys are still using trial-and-error methods, which is attributed to the much limited knowledge on the principles governing the heterogeneous nucleation behaviors and its effect on the co-precipitation crystallography. Using advanced transmission electron microscopy, the present project will study the microstructure evolution of the ageing Mg-Sn-Mn-Ag(-Zn) multi-component alloys to characterize the type, distribution and crystallographic characteristics of precipitates (or elements clusters) at different ageing stages in detail. Most attention will be paid on the microstructure features of the precipitates formed together and their nucleation features. Theoretically, the interface matching condition and the interfacial defects between co-precipitates and matrix will be analyzed using crystallography model combined with kinetic and thermodynamic factors. The interactions between the crystallography of co-precipitates and heterogeneous nucleation behaviors among different precipitates are expected to be elucidated, and new ideas on enhancing heterogeneous nucleation of precipitates by interface matching rules in precipitation-hardening alloys will be proposed. The result of the project will help us in understanding the interaction principles of various precipitates in multi-component alloys, and provide practical ideas on microstructure design of precipitation-strengthening Mg alloys.