An Investigation of Self-Propagating High Temperature Synthesis of Al–Al2O3 Composite Foam

Among all the conventional routes for the production of metal foams, combustion synthesis can yet be conducted as a novel method to produce self-propagating aluminum-alumina (Al–Al₂O₃) composite foams which are referred to as self-propagating high temperature synthesis (SHS). In this study, an aluminum matrix reinforced by submicron alumina particles was successfully fabricated via combustion synthesis through the reaction of aluminum (Al) powder and sodium nitrate (NaNO₃) powder as the blowing agent and the effect of their molar ratio on mechanical properties and the phase generated in the foam were investigated. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Image J software, X-ray diffraction (XRD), and compression mechanical test were utilized to study Al₂O₃ dispersion, matrix microstructure, elemental composition, pore size, final phases, and mechanical behaviour of the foams, respectively. According to the results, it was concluded that by increasing the molar ratio of aluminum in the precursors, the Al₂O₃ amount was decreased which was also confirmed by XRD results. Likewise, the combustion synthesis reaction was moderated followed by a decrease in the average pore size from about 40 to 21 µm. Study of pore morphology along with mechanical behaviour showed that the optimum molar ratio of the powders that produced open pores with an average size of 32 µm and an average plateau stress of 72 MPa through a sustainable combustion synthesis reaction was about NaNO₃ : Al = 2 : 13.3.