Relation Between Tensile Strut and Compressive Foam Deformation Behavior: Failure Mechanisms and the Influence of Dendritic Versus Globular Grain Structure in an AlSi7Mg0.3 (A356) Precision-Cast Open-Cell Foam

Open-cell aluminum foams are gaining importance for the design of lightweight structures and as electrodes in lithium-ion batteries. AlSi7Mg0.3 foams are produced by a modified investment casting process. By tuning the mold temperature, a change from the usual nearly monocrystalline dendritic to a polycrystalline globular grain structure is achieved. Tension and compression tests on single struts and foam specimens, respectively, are combined with digital image correlation, scanning electron microscopy, and phase contrast-enhanced microcomputed tomography in a synchrotron facility to correlate the mechanical properties and the failure mechanisms with the microstructure. The "globular" foams exhibit a lower strength and a less pronounced subsequent stress drop than the "dendritic" foams and the deformation mechanism changes from shear band-dominated failure to a layer-by-layer collapse, because of the lower strength and higher ductility of the "globular" struts. The "dendritic" struts have a more homogeneous microstructure, while the "globular" struts often contain silicon agglomerates in their central region. Accordingly, the latter struts exhibit a higher degree of scatter for the fracture strain. Thus, the arrangement of the silicon particles and the eutectic determines the mechanical properties on the strut level and thereby the failure behavior on the foam level. Adjusting the mold temperature of precision-cast open-cell AlSi7Mg0.3 foams modifies the microstructure from single-crystalline dendrites to globular grains and, concurrently, Si particle orientation and distribution change. All this results in higher ductility and lower strength of the globular struts and consequently, in a layer-by-layer collapse during foam compression, in contrast to the shear band-dominated failure of the dendritic foams.image (c) 2024 WILEY-VCH GmbH