析出相调控对中高含量稀土镁合金耐热性能的影响机制研究

Heat resistance is important performance index for the Mg-RE (rare earth) alloys. However, in order to improve the heat resistance of the Mg-RE alloys，plenty of rare earth elements are added to the Mg-RE alloys usually, resulting in considerable increasing of the cost and density of Mg alloy. The prismatic heat-resistant precipitates are the dominant strengthening phase for Mg-RE alloys in elevated temperature after T6 treatment. While the researches about “pyramidal precipitates” are quite absent. The research on the effect of Gd and Zn additions on microstructures and mechanical properties of Mg-4Sm-3Nd-Zr alloy was carried out by the proposer, the basal precipitates, prismatic precipitates and “pyramidal precipitates” (Zn-Zr binary phase) were introduced into the Mg-RE alloys after T6 treatment, which made a significant improvement of the ultimate tensile strength of the alloy in the elevated temperature. However, the researches on the precipitation mechanism of the crucial pyramidal Zn-Zr phase and how Zn-Zr phase affect the heat resistance of Mg alloy are still absent. In order to clarify above issues, the project would research the precipitation mechanism of the Zn-Zr phase by changing the content of Zn and Zr, and process of solution treatment. The effect of the Zn-Zr phase on tensile deformation mechanism of Mg alloy both at room temperature and elevated temperature would be researched in this project, as well as the effect on creep behavior of Mg alloy at elevated temperature. The objective of this project is improving the heat-resistance of Mg-RE alloy without increasing content of RE element, which is of importance to improve the utilization efficiency of rare earth resources and reduce the cost of Mg-RE alloy.

耐热性能是评价稀土镁合金性能的重要指标，然而稀土镁合金的高耐热性能多通过大量添加高成本稀土元素来实现，增加了合金的成本和密度。稀土镁合金主要通过时效析出的柱面和基面耐热相来强化合金高温强度，而有关“锥面析出相”的研究极少。申请人通过在Mg-4Sm-3Nd-Zr合金中添加微量的Gd和Zn元素，同时引入了基面、柱面析出相和锥面的Zn-Zr相，大大提高了合金的高温强度。然而合金中Zn-Zr相这一关键的“锥面析出相”的形成机制、及其对合金耐热性能的影响机制尚不明确。尚不能确保Mg-RE-Zn-Zr系合金固溶处理后Zn-Zr相一定形成。因此本项目拟通过调控Zn、Zr含量和固溶工艺来明晰Zn-Zr二元相的形成的固态相变机制，并研究析出相调控对镁合金变形机制和高温蠕变机制的影响。以期在不增加稀土元素含量的前提下，进一步提高合金的耐热性能，这对提高珍贵稀土资源的利用效率和降低稀土镁合金成本具有重大意义。

在项目执行的三年期间，完成了Zn-Zr相形成条件研究，总结出了Mg-RE-Zn-Zr体系合金中形成多种析出相的Zn和Zr元素的含量。通过细致地研究厘清了Mg-Sm-Gd-Zn-Zr合金中时效析出相类型。通过拉伸蠕变试验系统地研究了不同析出相与位错的相互关系，发现Zn-Zr相可以对蠕变过程中的位错运动起到很好的阻碍作用，而在由柱面析出相和基面析出相共同围成的“方形牢狱”中，位错线呈“C”字型分布，因此多种析出相协调作用下，对位错运动起到了有效的阻碍作用。得出少量Zn和重稀土元素添加能有效提高合金耐热性能的结论。可在不显著增加合金成本的前提下，进一步提高合金的耐热性能。这对于扩宽稀土镁合金的应用范围具有重要意义。依托本项目共发表论文9篇，申请发明专利2项，培养硕士研究生1名，培养博士后1名。