Optimization of the fatigue behavior of additively manufactured AlSi10Mg components using cryogenic finishing

• Applicants: Professor Dr.-Ing. Jan C. Aurich; Professor Dr. Eberhard Kerscher
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525766867

Laser beam melting (LBM) offers great potential as an additive manufacturing process due to the high design freedom, as well as the possibility of topology optimization. However, a comparatively poor fatigue behavior is present and the quality of the generated surfaces is insufficient for industrial applications. Therefore, additional post-processing is necessary. This increases the time required as well as the costs, which relativizes the advantages of LBM and inhibits further distribution of the process. The aim of this project is to realize a sufficient surface quality as well as an improved fatigue behavior in one process step. As a result, components manufactured by means of LBM are optimized with regard to the technical application requirements. Post-processing using cryogenic cooling offers the potential to improve not only the surface topography but also the mechanical and metallurgical properties of the components. This is due to the introduction of surface layer modifications that lead to an increase in hardness within the workpiece surface layer. Their formation is favored by low temperatures, as achieved when cryogenic cooling is used, in combination with high plastic deformation. The alterations within the workpiece surface layer have a positive effect on the fatigue behavior and thus on the service life and application behavior of the components. The improved application behavior and optimized surface topology result in increased added value, which can be realized in a single post-processing step. As a result, cryogenic machining offers the potential to compensate for the additional cost of post-processing, making the LBM process more lucrative for industry and research. In this project, the cryogenic post-processing of AlSi10Mg workpieces manufactured via LBM is investigated. The objective is to test the research hypothesis that cryogenic cooling during machining improves the surface morphology and thus the fatigue behavior of additively manufactured workpieces compared to dry machining. This hypothesis is investigated on a stress relieved, as well as a near-application, T6-treated condition. Machining tests are performed by varying the cryogenic cooling strategy, tool properties, and cutting parameters. Here, the relationships between the selected cutting parameters and the resulting thermo-mechanical load are recorded. The surface morphologies manufactured by cryogenic machining are then investigated with respect to their microstructure. Microstructural changes as well as hardness-depth curves are identified in relation to the respective varied thermo-mechanical load. The resulting fatigue behavior as a function of the generated surface morphology is then characterized. If the project is successful, recommendations for action can be derived from a final, holistic process analysis, which will enable optimization of the fatigue behavior of additively manufactured AlSi10Mg workpieces.

• DFG Programme: Research Grants