析出强化是镁合金重要的强化方式，弱的时效硬化（峰值硬度低或到达峰值时效时间长）效果极大地限制了析出强化型镁合金的发展和应用。针对这一问题，本项目利用应力时效改变析出相与镁基体的界面错配应变，调控析出相的析出特征，从而提高合金的时效硬化效果。围绕“应力诱导-析出相特征-时效硬化行为”关系，首先研究应力（大小、加载方式）加载对析出相尺寸、形貌、数密度及析出取向等特征的影响规律，阐明应力加载对析出相的形成及调控机理；其次定量分析应力时效过程中析出相的宏观特征及微观结构演变，结合不同特征析出相的强化模型，建立析出相强化与合金屈服强度的定量关系，揭示合金的时效硬化行为及强韧化机理，以期找到一种开发高强度、高韧性耐热镁合金的新策略和新技术。

Precipitation strengthening is an important strengthening method of Mg alloys. Weak ageing hardening effect (low peak-hardness or long peak-ageing time) greatly limits the development and application of precipitation-hardening Mg alloys. Concerning this issue, the project introduces stress ageing to improve the ageing hardening behavior of the alloy through altering the interfacial misfit strain of Mg matrix and precipitated phase to adjust the characteristics of precipitated phase. Centering on the relationship of “stress induction-precipitated phase characteristics-ageing hardening behavior”, firstly the influence of stress (magnitude, loading mode) on the characteristics of precipitated phase such as size, morphology, number density and precipitation orientation is investigated to clarify the formation and adjust rules of precipitated phase of Mg-Sn alloy under stress loading. Secondly, the quantitative relationship between precipitated phase strengthening and the yield strength of the alloy will be established based on strengthening mode of precipitation phase. Also, the ageing hardening behavior and toughness mechanism of alloy are investigated combined with the macro- and micro- structure evolution of precipitated phase during stress ageing. Finally, it expects to achieve a new strategy and technique to develop new heat resistance Mg alloys which bestows high strength and high toughness.