07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
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Item Open Access Local laser heat treatment of AlSi10Mg as-built parts produced by Laser Powder Bed Fusion(2024) Kramer, Steffen; Jarwitz, Michael; Schulze, Volker; Zanger, FrederikToday, complex structural components for lightweight applications are frequently manufactured by laser powder bed fusion (PBF-LB), often using aluminum alloys such as AlSi10Mg. However, the application of cyclic load cases can be challenging as PBF-LB produced AlSi10Mg parts typically have low ductility and corresponding brittle failure behavior in the as-built condition. Therefore, this paper presents investigations on the feasibility of a laser heat treatment of PBF-LB produced AlSi10Mg parts to locally increase the ductility and decrease the hardness in critical areas. Potential heat treatment process parameters were derived theoretically based on the temperature fields in the material calculated assuming three-dimensional heat conduction and a moving heat source. PBF-LB produced specimens were then laser heat treated at varying laser power and scan speed. Hardness measurements on metallographic cross sections showed hardness reductions of over 35 % without inducing hydrogen pore growth.Item Open Access Investigation of the formation and reduction of hydrogen porosity during laser welding of additively manufactured AlSi10Mg parts(2026) Kramer, Steffen; Lubkowitz, Victor; Haas, Michael; Michel, Johannes; Spurk, Christoph; Olowinsky, Alexander; Faria, Guilherme Abreu; Jarwitz, Michael; Graf, Thomas; Schulze, Volker; Zanger, FrederikWith the increasing industrial implementation of additively manufactured metal parts, the welding of such components gains importance. Due to size limitations of laser powder-bed fusion (PBF-LB) machines and design constraints, subsequent joining processes are required. However, the weld seam quality of PBF-LB manufactured parts, particularly aluminum parts, is still limited by pore formation in the weld seam. These pores are believed to be primarily caused by the agglomeration of hydrogen. Therefore, this study investigates the pore formation during laser beam welding of PBF-LB manufactured AlSi10Mg parts by means of in-situ high-speed synchrotron X-ray imaging. In addition, an in-situ laser powder drying process is investigated to reduce the hydrogen content of PBF-LB manufactured aluminum parts in order to prevent the formation of hydrogen porosity during the subsequent welding process. Results show that pores predominantly form in the interdendritic region at the solidification front due to the locally increased hydrogen concentration. By applying laser powder drying, the hydrogen content can be reduced by up to 25%, thereby effectively preventing the formation of hydrogen pores.Item Open Access Potential of contactless support structures for improving the part quality of AlSi10Mg PBF-LB parts(2023) Kramer, Steffen; Drechsel, Kai; Jarwitz, Michael; Schulze, Volker; Zanger, FrederikSupport structures are usually required to prevent thermally induced deformation of parts during the PBF-LB process, but also cause an increased effort for post-processing and an insufficient surface quality of the produced parts. An approach to overcome these limitations, suggested in the literature, is the use of contactless support structures (CSS), which should act as a heat sink to avoid thermally induced deformation. This approach was already successfully tested for electron beam melting (PBF-EB). Therefore, the aim of the present study is the experimental investigation of the application of CSS for the PBF-LB process. Different part and support geometries were built to investigate the potential of CSS to reduce thermally induced deformation during the PBF-LB process. Several use cases were covered, including increased overhang angles for thin features and maximized overhang thickness. The literature results for PBF-EB and Ti6Al4V could not be confirmed for PBF-LB using AlSi10Mg. The thermally induced deformation could not be reduced and the experimental results indicate that the use of CSS is accompanied by counterproductive process mechanisms.Item Open Access Impact of different pore types on the tensile and fatigue properties of AlSi10Mg parts produced by laser powder bed fusion(2025) Kramer, Steffen; Wexel, Helena; Purwitasari, Anisa; Jarwitz, Michael; Schulze, Volker; Zanger, FrederikThe mechanical properties of laser powder bed fusion (PBF-LB) parts such as fatigue strength or tensile strength are greatly influenced by the porosity occurring in the material. While it is common to achieve relative densities over 99.5% for the aluminum alloy AlSi10Mg, in practice, the formation of statistically occurring oxide pores cannot be avoided completely. Due to their irregular shape, these pores are detrimental for the mechanical properties. It is hypothesized that oxide pores can be avoided by increasing the energy input. This in turn leads to the formation of spherical keyhole pores. However, it is not sufficiently understood how keyhole porosity affects the mechanical properties with regard to oxide pores. Therefore, this work investigates the impact of keyhole pores, lack of fusion pores and oxide pores on the mechanical properties of PBF-LB AlSi10Mg parts. Results show the importance of single critical defects for the fatigue behavior compared to the impact of relative porosity and reveal the less detrimental nature of keyhole pores compared to oxide pores. Despite a much higher relative porosity, the tensile strength of specimens containing keyhole pores is comparable to that of highly dense parts whereas the fatigue strength has even improved.