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

Abstract

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 modified 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.