压铸Mg-Al-RE系合金强化机理和蠕变机制的研究

Due to their outstanding high temperature properties and creep resistance, high-pressure die-cast (HPDC) Mg-Al-RE based alloys possess huge application market and high values in the energy saving automobile materials and the advanced rail transit equipment materials. Nonetheless, due to the complexity of the microstructures of the Mg-Al-RE based alloys and the limitation of the conventional creep mechanism analysis (CMA) method, their strengthening mechanisms and creep mechanisms are still ambiguous, which seriously impede the further improvement of the Mg-Al-RE based alloys. Using experimental methods, this project puts forwards quasi-single-variable controlling the components, morphologies, contents, sizes and distributions of the Al-RE phases, and then systemically studying the effect on strength and creep properties of every characteristic factor of the Al-RE phases. Finally, using statistic analysis method on the experimental data and combined with the current strengthening theory and models, this project plans to build the strengthening mechanisms of the Mg-Al-RE based alloys. Simultaneously, based on the investigations dealing with the microstructural evolution process during creep deformation, we plan to illuminate why the conventional CMA method cannot reasonably analyze the creep mechanisms of the HPDC Mg-Al-RE based alloys. Furthermore, through the integration method for various creep mechanisms, this project tries to build a new method for reasonably dealing and analyzing the creep data of the HPDC Mg-Al-RE based alloys. This project can provide insight and new idea into alloy design principles for higher performance Mg-Al-RE based alloys, and also provides important data for developing and designing high performance Mg-Al-RE typed products in power train components.

压铸Mg-Al-RE系合金的优异高温性能和抗蠕变性能使得其在节能汽车材料和先进轨道交通装备材料等领域具有巨大的应用市场和价值。但由于该系合金的微观组织复杂和蠕变机制分析方法的局限性，其强化机理和蠕变机制目前尚不清楚，从而限制了该系合金的进一步发展。本项目拟通过实验方法，对Al-RE相的组分、形貌、含量、尺寸和分布进行准单变量控制，然后系统研究Al-RE相各特征因素对合金强度和蠕变性能的影响及规律。最后通过数据统计分析方法，结合现有强化理论和模型，建立压铸Mg-Al-RE系合金的强化机理；同时通过研究蠕变过程中微观组织演变，阐明传统蠕变数据分析方法不能正确分析压铸Mg-Al-RE合金蠕变机制的问题，并采用整合多种蠕变机制的方法，建立合理的蠕变数据处理和分析方法。本项目为开发高性能Mg-Al-RE系合金提供理论指导和新的思路，并为研发和设计高性能Mg-Al-RE型传动零部件产品等提供重要数据。

压铸Mg-Al-RE合金具有优异的耐热性能，在汽车、电子3C等领域具有巨大的应用前景。但是其强化机理和蠕变机理尚缺乏系统的研究。本项目设计并制备了一系列具有不同微观组织的Mg-Al-RE合金，系统深入地研究了合金的强化机理和蠕变机制，揭示了Al-RE相结构及形貌对合金力学性能和蠕变性能的影响；我们发现了一种新的Al-RE相，eta-Al3La, 其具有非常好的强化效果，同时可以传递<c + a>位错，在一定程度上减轻了了第二相周围的应力集中，因此合金表现出极好的强塑平衡性能，同时还有很高的抗蠕变性价比。此外，该合金的导热系数达到了126W/(m.K)，是目前压铸合金中导热系数最高的合金，为我们开发新型高强高导热压铸镁合金提供了理论指导。针对Mg-Al-RE合金的非常规蠕变行为及高蠕变应力指数，我们通过系统的TEM位错亚结构表征，发现了其蠕变行为是由传统蠕变行为和回复行为共同作用的结果。回复行为主要包括位错带诱导孪晶形核及长大、<c + a>位错塞积诱导亚晶界形成。回复行为会极大地降低位错密度，产生加大的流变速率，因此导致合金蠕变速率急速攀升。对传统Mg-Al-RE合金的蠕变研究结果表明，合金的蠕变应力指数从5到23，到38后突然下降至8，然后又急速上升至45，表现出无规律的特点。但通过引入动态回复的影响，其蠕变应力指数在蠕变应力较低时为5，在蠕变应力较高时为8，分别对应位错滑移和位错攀移两种蠕变机制。这也为我们研究镁合金蠕变行为提供了新的思路和方法。