Mechanism-based characterization and evaluation of the performance of resistively sintered semi-finished products based on recycled aluminum chips

• Applicants: Professor Dr.-Ing. Bernd-Arno Behrens; Professor Dr.-Ing. Frank Walther
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 454199925

Due to increasing resource scarcity, demands for energy-efficient recycling of aluminum (Al) are of rising interest. Direct solid-state recycling of aluminum chips promises significant energy savings compared to traditional re-melting recycling processes while reducing material loss due to burn-off. In the second phase of the research project, expanded research questions regarding the recycling of aluminum chips and related properties take are focused. While the first phase focused on elucidating fundamental mechanisms and cause-and-effect relationships, significantly improving the quality of the weld seams between the chips concerning oxide breakdown, the second phase aims to jointly consider the chip boundaries and the material itself. The overarching goal of the research project is the development and characterization of a process for integrated heat treatment during the recycling of aluminum chips based on the mechanism-based process-structure-property relationship. Research questions to be considered primarily concern the combination of sintering and forming and the interaction of different strengthening methods during heat treatment. The integrated heat treatment approach presented offers innovative potential, far beyond the state of the art, to avoid subsequent energy-intensive heat treatments. It combines the precipitation hardening with the cold hardening introduced in the forming process. This allows for the generation of application-specific material properties that are entirely unexplored for chip-based materials. By using hybrid components, properties such as ductility and strength of different alloys can be combined in a single component. In addition to tensile and fatigue tests for mechanical characterization, multiaxial studies are conducted to establish a damage model for the produced components. These are complemented by metallographic methods, combined with FIB-SEM (Focused Ion Beam Scanning Electron Microscopy) analyses for detailed examination of the chip boundaries, as well as computed tomography measurements for defect structure determination to ensure material characterization depending on the process parameters used. From a societal and political perspective, the project holds high relevance, as, in addition to significant energy savings, further saving potential can be realized by the use of process heat. Moreover, beyond the production of semi-finished products achieved in the first phase, components close to their final shape are directly produced, eliminating the otherwise necessary forming operation, also in the interest of energy and resource conservation.

• DFG Programme: Research Grants