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

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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.