Collaborative Research: Fundamentals of Material Behavior and Structure in Making Laminated Metal Composites with Assistance of Electrical Current in Bonding Operation

层合金属复合材料对于减轻运输车辆的重量和能源需求至关重要。然而，这些复合材料的制造难度大、成本高、耗能大。为了制造层状金属复合材料，现有的方法包括通过变形过程施加较大的应力或压力来粘结多个金属板。使用加热可以在制造过程中软化金属板，减少所需的作用力。一种可能更便宜、能源密集度更低、更容易控制的方法是使用外加电流而不是纯热。在变形过程中将电流驱动到金属零件中的行为可以将热量精确地定位到需要它的地方，从而在制造过程中暂时软化金属。然而，局部电流如何以及为什么会软化金属并不完全清楚，特别是在同时施加力的情况下。该奖项支持基础研究，以了解金属在电流和压力同时作用下是如何软化和结合的。这样的理解将使制造工艺的开发能够生产出更便宜、更高质量的叠层金属复合材料。反过来，这将促进低成本生产具有更高燃油效率的运输工具，包括飞机和汽车。研究目标是通过微观和细观尺度的研究，揭示在电流和机械载荷联合作用下与降低材料流动应力相关的基本现象。在这项研究中，将在西北大学进行层合金属复合材料的电辅助静电连接。层状金属复合材料将在一定范围的压力和连续电流条件下制备。然后将测试这些样品的质量，即结合强度，并通过先进的表征技术进行分析。这些由卡内基梅隆大学进行的表征方法将使用电子显微镜将金属微结构的各个方面与结合强度相关联，并确定电子辅助变形机制。此外，还将在显微镜内进行实验，以可视化在原位施加持续电流和压力下金属变形的动力学。这些实验将对电流对微结构、变形行为和金属结合的影响提供新的理解。

Laminated metal composites are critical to reducing the weight and energy demands of transportation vehicles. However, the manufacture of these composites is difficult, costly, and energy intensive. To make laminated metal composites, existing methods involve applying large stresses or pressures to bond multiple metal sheets through a deformation process. Using heat can soften the metal sheets during manufacturing, reducing the amount of required force. A potentially cheaper, less energy intensive, and more controllable approach is to use applied electrical current instead of pure heat. The act of driving electrical current into a metal part during deformation can localize the heat to exactly where it is needed, temporarily softening the metal during a manufacturing process. However, how and why local current flow softens metals is not completely understood, particularly when force is simultaneously applied. This award supports fundamental research to provide the understanding of how metals soften and bond under simultaneous electrical current and pressure. Such understanding will enable the development of manufacturing processes that produce cheaper and high quality laminated metal composites. In turn, this will facilitate low-cost production of transportation vehicles with better fuel efficiency, including aircraft and automobiles.The research objective is to uncover the fundamental phenomena associated with the reduction of material flow stress under the combined electrical current and mechanical loads through the investigations at the micro- and meso- scales. In this study, electrically-assisted static bonding of laminated metal composites will be carried out at Northwestern University. Laminated metal composites will be fabricated under a range of pressure and continuous electrical current conditions. These samples will then be tested for quality, in terms of bond strength, and analyzed by advanced characterization techniques. These characterization approaches, carried out at Carnegie Mellon University, will use electron microscopy to correlate aspects of the metal microstructure to bond strength and to determine electrically-assisted deformation mechanisms. Furthermore, experiments will be conducted inside the microscope in order to visualize the dynamics of metal deformation under in situ applied continuous electrical current and pressure. Such experiments will provide new understanding on the effects of electrical current on microstructures, deformation behavior, and metal bonding.