Ultrafine-grained Magnesium Alloys Manufactured by Multi-axial Forging: Elucidating Mechanisms of Achieving Both High Strength and High Ductility

镁合金具有高比强度、比刚度、良好的减振减震能力、高导热系数等一系列吸引人的性能，在汽车、航空航天、包装等领域具有广阔的应用前景。然而，由于镁合金固有的原子级结构，高强度镁合金的热机械加工是一个挑战，这使得它们很难在常温下塑性变形成高性能的产品。该奖项旨在通过高温多轴锻造工艺的基础研究来解决先进的高强度镁基合金加工中的挑战，以获得对复杂金属变形行为中的工艺-结构-性能关系的科学理解。这项研究有可能加快镁合金的部署步伐，并促进具有成本效益的轻量化结构制造，例如，允许更薄的部件或部件在运输部门实现更好的燃油经济性。在这个项目中，研究生和本科生将接受先进制造科学的培训，加工概念也将整合到现有的制造课程中。此外，在工程日和校园职业日举办先进制造开放日将培养中学生对先进制造职业道路的认识。本项目的研究目标是了解与多轴锻造相关的先进加工概念，以顺序地制造具有非常高强度和高延展性的超细晶轻质镁合金。多轴锻造的工艺-组织-性能研究，通过改变每道次的应变，将通过阐明影响力学性能和变形机制的晶界特征分布与晶粒取向相关性之间的关系，来解决镁合金织构相关各向异性的关键问题。此外，通过发现晶粒取向分布与从超细晶到粗晶相对较宽的组织谱中的塑性机制之间的定量关系，还将揭示高强镁合金高塑性的力学基础。这将通过结合纳米压痕实验、电子背散射衍射和变形晶粒的事后电子显微镜来研究每道次应变对镁合金成形性的依赖关系来实现。此外，还设想了一种机器学习方法，用于建立晶粒取向分布和延展性之间的定量关系，作为每道次应变的函数，以加速镁基合金的加工。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Magnesium alloys exhibit a number of attractive properties including high specific strength and specific stiffness, good damping and shock absorbing capacity, and high thermal conductivity, etc., appealing for the use in automobile, aerospace, and packaging industries. However, thermo-mechanical processing of high-strength magnesium alloys is a challenge because of the inherent atomic-scale structure, which makes them difficult to plastically deform into high performance products at normal temperatures. This award addresses the challenge in processing of advanced high-strength magnesium-based alloys by fundamental research of the multi-axial forging process at high temperatures to attain scientific understanding of the process-structure-property relationship in complex metal deforming behaviors. The research has a potential to accelerate the pace of deployment of magnesium alloys and to promote cost-effective lightweight structure manufacture, allowing, for example, thinner sections or components to achieve better fuel economy in the transportation sector. In this project, graduate and undergraduate students will be trained in advanced manufacturing science and the processing concepts will also be integrated in the existing manufacturing curriculum. Furthermore, hosting of advanced manufacturing open house on the Engineering Day and Career Days on campus will foster awareness of advanced manufacturing career pathways in middle and high school students.The research objective of this project is to understand advanced processing concepts associated with multi-axial forging, in a sequential manner, in fabricating lightweight magnesium alloys with ultrafine grains that are characterized by a combination of very high strength in conjunction with high ductility. The process-structure-property study of multi-axial forging, by changing the strain per pass, will address the critical issue of texture-related anisotropy in magnesium alloys through elucidating the relationship between the orientation dependence of grains and the grain boundary character distribution that affect the mechanical properties and deformation mechanisms. In addition, the mechanistic basis of high ductility in high strength magnesium alloys will be unraveled through the discovery of quantitative relationship between the orientation distribution of grains and the plasticity mechanisms in a relatively wide grain-structure spectrum from ultrafine-grained to coarse-grained structures. This will be accomplished by studying the dependence of strains per pass on the formability of magnesium alloy by combining nanoindentation experiments with electron back scattered diffraction and post-mortem electron microscopy of deformed grains. Moreover, a machine learning approach for a quantitative relationship between the orientation distribution of grains and the ductility as a function of the strain per pass is envisaged to accelerate the processing of magnesium-based alloys.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.