Collaborative Research: A Theoretical and Experimental Study of Mechanical Properties in Ultrafine-Grained Alloys

镁合金是所有结构金属材料中最轻的，由于其低密度、中等强度和刚度、可用性和可回收性的结合而越来越受到人们的关注。特别是，这些特性与汽车、铁路和航空航天工业直接相关，这些工业寻求用较轻的部件取代较重的部件，从而最大限度地减少燃料的使用。尽管人们对镁合金的兴趣越来越大，但镁合金的强度不够，更重要的是，镁合金的部件必须在非常高的温度下加热和成型，这对运输制造商来说在经济上是不允许的。该奖项支持基础研究，以获得能够协同提高强度和降低加工温度到环境温度的知识，从而同时解决两个重要的使用障碍。这项研究将以高度相关的方式在材料科学，力学和制造的边界上交叉。它将吸引、教育和使学生从代表性不足的群体中获得知识和信心，以直接满足美国工业和政府对节能运输中轻质材料的严格和不断变化的需求。由于缺乏必要的主动滑移系统，铸造镁合金的环境温度塑性较差。这个问题在变形加工合金中更为复杂，其中高度各向异性织构限制了均匀的材料流动。另一方面，晶粒尺寸小于100nm的纳米晶材料与粗晶材料相比，具有特殊和理想的性能，包括强度和延展性的同时增加。基于此，本项目的目标是：1)利用新颖的加工方法和基于微观结构的建模，揭示大块、全致密、纳米镁合金在环境温度下塑性的基本机制；2)利用后续知识可预测地设计和制造低温可成形镁合金。就更广泛的科学影响而言，一个易于处理和系统的实验和建模框架的发展将代表着目前设计具有定制微观结构的纳米合金的半经验方法的重大进步。

Magnesium alloys are the lightest of all structural metallic materials, and are becoming of increasing interest due to their combination of low-density, moderate strength and stiffness, availability and recyclability. In particular, these properties are of direct relevance to the automobile, rail and aerospace industries that seek to replace heavier components with lighter ones, and thus minimize fuel usage. Despite the increased interest, magnesium alloys suffer from not being strong enough, and more so, that components have to be heated and shaped at very high temperatures, which is economically prohibitive for transportation manufacturers. This award supports fundamental research to acquire knowledge that will enable synergistic increases in strength and lowering of the processing temperature to ambient temperatures, thereby solving two important barriers to usage at one time. This research will intersect at the boundaries of materials science, mechanics and manufacturing in a highly relevant way. It will attract, educate and enable students from underrepresented groups to gain the knowledge and confidence to directly address the rigorous, evolving needs in U.S. industry and government for lightweight materials in energy efficient transportation. Cast magnesium alloys have suffered from poor ambient temperature plasticity due to the lack of necessary active slip systems. This problem is compounded in wrought processed alloys wherein highly anisotropic textures limit uniform material flow. On the other hand, nanocrystalline materials with grain sizes below 100nm have exceptional and desirable properties when compared to their course-grained counterparts, including concurrent increases in strength and ductility. Motivated by this, the goals of this project are 1) to uncover the underpinning mechanisms for ambient temperature plasticity in bulk, fully dense, nano-grained magnesium alloys using novel processing approaches and microstructure-based modeling; and 2) to exploit the subsequent knowledge to predictably design and fabricate low-temperature formable magnesium alloys. In terms of broader scientific ramifications, the development of a tractable and systematic experimental and modeling framework will represent a major advance over current semi-empirical methods for designing nano-grained alloys with tailored microstructures.