Synthesis and Characterization of Al Chip-Based Syntactic Foam Containing Glass Hollow Spheres Fabricated by a Semi-Solid Process

In this study, aluminum (Al) chip matrix-based synthetic foams were fabricated by hot pressing at a semi-solid (SS) temperature. The densities of the foams ranged from 2.3 to 2.63 g/cm³, confirming that the density decreased with increasing glass hollow sphere (GHS) content. These values were approximately 16% lower than the densities of Al chip alloys without GHS. The Al chip syntactic foam microstructure fabricated by the semi-solid process comprised GHS uniformly distributed around the Al chip matrix and a spherical microstructure surrounded by the Mg₂Si phase in the interior. The resulting spherical microstructure contributed significantly to the improvement of mechanical properties. Mechanical characterization confirmed that the Al chip syntactic foam exhibited a compressive strength of approximately 225-288 MPa and an energy absorption capacity of 46-47 MJ/M³. These results indicate higher compressive properties than typical Al syntactic foam. The Al chip microstructure, consisting of the Mg₂Si phase and GHS, acted as a load-bearing element during compression, significantly contributing to the compressive properties of the foam. An analysis was performed using an energy-dispersive spectrometer to validate the interfacial reaction between the GHS and the matrix. The results showed that MgAl₂O₄ was uniformly coated around GHS, which contributed not only to the strength of the matrix, but also to the mechanical properties via the appropriate interfacial reactive coating.