基于双组态晶粒结构的新型Mg-Al-Ce变形镁合金的高强高塑化机理研究

Currently, it is the effective route to expand applications of Mg alloys by developing newly low-cost Mg alloy systems with both high strength and good ductility. According to the newly found high-strength-ductility Mg-6Al-2Ce(wt.%) with ultimate strength of 370MPa and elongation of ~10%, and the complicated microstructure with both nano-phases and bimodal grain structures, the project would firstly characterize structure of nano-phases and morphology of dislocations. The dynamic precipitation, dislocations activations and interactions, nucleation and growth of subgrains during extrusion of Mg-Al-Ce alloys would be investigated. Relationship between extrusion parameters and grains size of as-extruded Mg-Al-Ce alloys would be also studied, to illustrate dynamic recrystallization mechanism of present alloys. During tensile testing of as-extruded Mg-Al-Ce alloys, internal dislocations nucleation and growth in the coarse/fine grain interiors, and also the interactions between dislocations and nanophases would be studied. The stress and strain partitioning and co-deformation behaviors between coarse and fine grains would also be investigated to clarify the reason of high strength and ductility. The present project would not only clarify high strength and ductility mechanism of present alloy with bimodal grain structure and nano-phases, but also can provide meaningful basis for designing other newly low-cost Mg alloys.

开发出新型的低成本和高强高塑性兼备的镁合金体系是解决目前镁合金应用范围仍然较小的有效途径。根据最近发现的高强塑Mg-Al-Ce合金(抗拉强度370MPa，延伸率~10%)以及复杂的纳米相和双组态晶粒等多相共存的微观组织，本项目拟对挤压态Mg-Al-Ce合金的微观结构进行精细表征(纳米相和位错等)；研究Mg-Al-Ce合金在挤压过程中第二相的动态析出、位错的启动和交割、亚晶的形核和长大等，明晰合金动态再结晶的微观机制；研究挤压态Mg-Al-Ce合金在拉伸过程中，粗/细晶内部位错的形核和扩展以及位错同纳米相之间的交互作用，粗/细晶粒之间的应力应变配分和协调变形行为，以期阐明挤压态合金获得高强高塑力学性能的微观机理。通过本项目的实施，不仅可以解析Mg-Al-Ce合金中的双组态晶粒组织以及纳米相实现镁合金高强塑化的微观机制，同时可以为设计其他新型低成本高性能的镁合金提供有益的参考。

开发出新型的低成本和高强高塑性兼备的镁合金体系是解决目前镁合金应用范围仍然较小的有效途径。本项目开采用传统一步挤压方法，制备出了高强塑兼备的微合金化Mg-Al-Ce变形合金。合金的晶粒细化至超细（平均晶粒尺寸为420nm）状态，且该合金的微合金化含量极低，合金化元素Al和Ce的总含量仅~0.35%，但合金具有高的屈服强度，达到了~365MPa。项目对挤压态Mg-Al-Ce合金的微观结构进行精细表征(析出相和位错等)；研究Mg-Al-Ce合金在挤压过程中第二相的动态析出、位错的启动和交割、亚晶的形核和长大等，明晰合金动态再结晶的微观机制；研究挤压态Mg-Al-Ce合金在形变过程中，粗/细晶内部位错的形核和扩展以及位错同析出相之间的交互作用；期阐明了挤压态合金获得高强高塑力学性能的微观机理。微观组织分析显示，该合金超细晶组织个形成与Al和Ce元素在位错和晶界上的偏聚行为相关，因为元素偏聚会在合金挤压过程中阻碍晶粒生长。向Mg-0.2 wt.%Al合金中添加微量的Ce元素（~ 0.15 wt.%）能促进富Ce-Al团簇的形成，纳米团簇沿位错分布，这可有效抗衡挤压过程中的热能激活位错回复，保证了晶粒细化。密度泛函理论的计算结果进一步证实了Al和Ce元素的共偏聚在能量上是更有利的，这与Al和Ce原子之间的大尺寸错配和负混合焓密切相关。更重要的是，这种Ce-Al共偏析可以大大强化镁合金的晶界，从而提高镁合金的屈服强度。现有镁合金中由于线性和平面共偏析而产生的新的晶粒细化机制，为其它金属材料获得较低的微合金化含量和较高的强度提供了重要的理论指导（如在Mg-Nd系和Mg-Ca系合金中实现了高性能合金设计目标）。通过本项目的实施，不仅可以解析Mg-Al-Ce合金中的双组态晶粒组织以及纳米相实现镁合金高强塑化的微观机制，同时可以为设计其他新型低成本高性能的镁合金提供有益的参考。