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，由于其密度低、强度和刚度适中、可利用性和可回收性的组合而受到越来越多的关注。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，从而将燃料使用量降至最低。尽管人们对镁合金的兴趣与日俱增，但镁合金的强度还不够高，更严重的是，零部件必须在非常高的温度下加热和成形，这对运输制造商来说在经济上是行不通的。该奖项支持基础研究，以获得能够协同提高强度和将加工温度降低到环境温度的知识，从而同时解决两个重要的使用障碍。这项研究将以一种高度相关的方式交叉于材料科学、力学和制造的边界。它将吸引、教育和使来自代表性不足群体的学生获得知识和信心，以直接满足美国工业和政府对节能交通中不断变化的轻质材料的严格需求。由于缺乏必要的活动滑移系统，铸造镁合金的常温塑性较差。在高度各向异性织构限制均匀材料流动的变形加工合金中，这个问题变得复杂起来。另一方面，与粗晶材料相比，晶粒度小于100 nm的纳米晶材料具有优异的性能，包括同时提高强度和延展性。基于此，本项目的目标是：1)利用新的加工方法和基于微观结构的建模，揭示块体、全致密、纳米晶镁合金室温塑性的支撑机制；2)利用后续知识来设计和制造可预测的低温可成形镁合金。在更广泛的科学分支方面，一个易于处理和系统的实验和建模框架的开发将代表着比目前设计具有定制微结构的纳米晶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.