Solid-state bonding of oxide-covered aluminium surfaces in metal forming

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Solid-state bonding is a physical process by means of which material composites can be produced by applying pressure to two surfaces. By definition solid-state bonding takes place at a temperature below the melting temperature of the composite partners and without the addition of a filler material.Forming processes in which the pressures and surface expansions required for solid-state bonding are achieved include roll cladding, accumulative roll bonding and hot extrusion, as well as recycling processes for the direct recycling of aluminium scrap. So far, the processes have only been researched with regard to their process-specific parameters and their influence on the resulting bond. Up to now, there is no sufficient transferability of the physical relationships. This transferability is sometimes also lacking within individual process classes, since the forming conditions in the welding zone are often not exactly known. Currently no generally applicable physical models for weld strength prediction exist, which are capable of producing precise results over the entire relevant range of temperatures and strain rates. Furthermore, there are no experimental methods for determining local welding strengths.The goal of the research project is the quantitative determination of the influence of physical factors on the local welding of oxide-covered surfaces. For this purpose, experimental methods for determining a local weld strength are derived and calculation methods for predicting the weld strength depending on the forming conditions in the weld zone are developed. To produce weld seams, an experimental method based on hot extrusion is to be used, which allows the targeted welding of two oxide-covered surfaces under known forming conditions as well as sample extraction with a known weld seam position. The knowledge gained is used to generalize and validate existing welding models. Finally, methods are derived to promote welding of oxide-covered surfaces.