微量钇对高屈服强度Mg-Al-Ca-Mn合金增塑作用及机制的研究

高屈服强度Mg-Al-Ca-Mn（AXM）系变形镁合金塑性一般相对较差，制约了这类新型高强镁合金的应用，其在凝固-挤压后会残留大量、多种类未溶结晶第二相，而相内及相界邻域的应变局域化是导致其低塑性的关键诱因之一。合理的微合金化可提高塑性，研究表明微量钇元素对镁基体的增塑作用明显，但其能否提高结晶第二相的塑性并促进相间协调变形尚不明确。本项目拟采用先进的原位定量力-热耦合测试技术，在室温至300℃及不同应变速率下，系统研究微量钇元素添加前后AXM合金中结晶第二相的塑性变形行为及相间协调变形行为，分析含相界面变形体在均匀塑性变形阶段微观缺陷演化规律及机制，揭示温度和应变速率耦合作用下相界面邻域变形机制（位错、孪生）的协同规律，澄清微量钇固溶原子对上述微观缺陷和相间协调变形的影响，阐明钇微合金化对AXM合金增塑的微观调控机理，以期为研发兼具高强度和高塑性的AXM系镁合金提供基础理论指导。

Poor ductility of the high-yield-strength AXM wrought Mg alloys has restricted their wide application. The large amount and various kinds of the dispersive secondary phases will form in AXM alloys during the solidification-then-extrusion process. Strain localization tends to occur in the inside of secondary phases and the adjacent zone of phase interface, which plays an important role in the origin of the low ductility. It is suggested that yttrium element exhibits remarkable ductilizing effect on the Mg matrix, while it is not yet clear that if the yttrium microalloying can improve the ductility of the secondary phase and the coordinated plastic deformation near the phase interface. In this project, the thermo-mechanical coupling, in-situ, and quantitative nanomechanical testing will be performed on both AXM and yttrium microalloyed AXM wrought Mg alloys. The plastic behavior of the secondary phase and coordinated plastic deformation mechanisms near the phase interface will be investigated at temperatures ranging between room temperature and 300℃ and different strain rates. The mechanisms of the microscopic defects evolution during deformation will be analyzed. This can help to reveal that the coordinated movement of the deformation carriers (dislocation, twin, etc.) in the adjacent zone of phase interface under the temperature-strain rate coupling. Furthermore, the regulation mechanism of the yttrium microalloying on the coordinated deformation near phase interface and the micro-defects evolution will be elucidated as well. Finally, a systematic micro-regulation theory of the yttrium microalloying ductilizing will be established to lay a theoretical foundation of the ductilizing design for the high-yield-strength AXM series Mg wrought alloys.