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    Analyzing the influence of the investment casting process parameters on microstructure and mechanical properties of open-pore Al–7Si foams
    (2023) Firoozbakht, Mahan; Blond, Aurelien; Zimmermann, Golo; Kaya, Ali Can; Fleck, Claudia; Bührig-Polaczek, Andreas
    Aluminum alloy foams with high specific compressive strength and good energy absorption capacity are widely used as structural materials and shock absorbers. The investment casting process offers an interesting opportunity for the production of open-pore aluminum foams. However, foam casting differs from casting of solid parts, and there is a lack of practical knowledge about the microstructure tuning of the ultra-thin cast struts. Our study focuses on the influences of the casting conditions such as mold temperature on the microstructure and consequently on the mechanical properties of aluminum-silicon alloy foams. We investigated microstructural features using various metallography techniques and defined mechanical properties under uniaxial compression test. Here, we observed improvements in the strut microstructure together with decrease of the mold filling by reduction of the mold temperature. Microstructure improvements involve transformation of a single dendritic aluminum grain in each strut to globular grains along with a more homogeneous distribution of the silicon particles across the strut cross-section. These changes bring higher ductility and energy absorption efficiency to the foams, which are evident from the smoother plateau of the stress-strain curves. Decline of the mold filling, on the other hand, has negative effect on the overall mechanical properties.
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    Öğe
    Modification of open-cell cast aluminum-silicon foams with strontium
    (2024) Kaya, Ali Can; Firoozbakh, Mahan; Buehrig-Polaczek, Andreas; Blond, Aurelien; Fleck, Claudia
    The mechanical properties of open-cell aluminum foams can be influenced by enhancing the microstructure of the struts. The foams produced by investment casting face slow cooling rates, which makes it challenging to improve the morphology of the phases. In the case of aluminum silicon cast foams, the silicon phase accumulates on the surface of the struts, which leads to brittle fractures. In the present study, we successfully modified the silicon phase in open-cell AlSi7Mg and AlSi10Mg cast foams by adding strontium and investigated the influence of the strontium content on the microstructure and mechanical properties at the foam and strut levels. Despite the cooling rates of less than 0.5 ?C/s during solidification, the strontium addition of 200–800 ppm effectively decreased the size of the silicon particles and improved their distribution in the micrometer-sized struts. Improvements in the compressive properties of the foams and the tensile properties of the struts only occurred at the strontium levels of 200 and 400 ppm. The effective modification in this casting condition is due to the limited solidification space, which favors the formation of the atomic clusters responsible for the modification
  • Küçük Resim
    Öğe
    Relation between Tensile Strut and Compressive Foam Deformation Behaviour: Failure Mechanisms and the Influence of Dendritic Versus Globular Grain Structure in an AlSi7Mg0.3 (A356) Precision?Cast Open?Cell Foam
    (2024) Kaya, Ali Can; Blond, Aurelien; Firoozbakht, Mahan; Bührig-Polaczek, Andreas; Fleck, Claudia
    Open-cell aluminum foams are gaining importance for the design of lightweightstructures and as electrodes in lithium-ion batteries. AlSi7Mg0.3 foams areproduced by a modi?ed investment casting process. By tuning the mold tem-perature, a change from the usual nearly monocrystalline dendritic to a poly-crystalline globular grain structure is achieved. Tension and compression tests onsingle struts and foam specimens, respectively, are combined with digital imagecorrelation, scanning electron microscopy, and phase contrast-enhancedmicrocomputed tomography in a synchrotron facility to correlate the mechanicalproperties and the failure mechanisms with the microstructure. The “globular”foams exhibit a lower strength and a less pronounced subsequent stress dropthan the “dendritic” foams and the deformation mechanism changes from shearband-dominated failure to a layer-by-layer collapse, because of the lower strengthand higher ductility of the “globular” struts. The “dendritic” struts have a morehomogeneous microstructure, while the “globular” struts often contain siliconagglomerates in their central region. Accordingly, the latter struts exhibit a higherdegree of scatter for the fracture strain. Thus, the arrangement of the siliconparticles and the eutectic determines the mechanical properties on the strut leveland thereby the failure behavior on the foam level.