Metal matrix syntactic foams represent a highly relevant subject in the research field of closed-cell metal-ceramic composite foams. The composite nature of the material, with ceramic hollow spheres embedded within a metal matrix, represents a porous structure with superior strength in comparison to conventional metal foams, making them suitable for the use in a wide range of structural applications.

Al-based metal matrix syntactic foams are most commonly investigated, as they provide a high potential due to the combination of brittle ceramic hollow spheres with a ductile and low-density Al matrix. The possibility to change the compounds’ interface and matrix properties by the presence of Mg in the matrix, enables an easy way to influence the foam’s key aspects of porosity, microstructure and mechanical properties under compressive loading, starting at the production.

Since past studies have solely investigated simple combinations of Al-based matrices and ceramic hollow spheres, there still is a huge research potential in studying the impact of different Mg contents in AlMg-based syntactic foams. Results from the microstructural characterization are compared with results of the compressive testings, in order to gain a holistic understanding of the influence of the Mg content on the interface and microstructure of AlMg-Al₂O₃/SiO₂ syntactic foams and their respective mechanical behavior under compressive loading. For this reason, syntactic foams, made of AlMg alloys with different Mg contents (min. 5 wt%) and two different kinds of oxide ceramic hollow spheres (Al₂O3 and Al₂O₃/SiO₂), are produced, using a vacuum-pressure infiltration casting technique. The modification of the Mg fraction positively influences the wetting behavior of the different ceramic spheres, resulting in a change of the metal-ceramic interfacial phase composition as well as the microstructure of the base matrix, investigated by light microscopy, scanning electron microscopy (SEM-EDS) and x-ray diffraction (XRD). The main reactions of SiO₂ with AlMg with higher Mg contents show the strongest impact on the microstructural change, by forming a diffusion zone on the interface with brittle oxides, silicides and ternary phases. In combination with the change of ductility and strength of higher Mg contents in the AlMg matrix, a strong dependence on the macroscopic deformation behavior can be detected.