Reaction mechanism and mechanical properties of an aluminum-based composite fabricated in-situ from Al-SiO2 system

An (α-AlO + Si)/Al composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and SiO. The synthesis mechanism and resulting microstructure of the composite were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray energy dispersive spectroscopy (EDS). It was found that when the reinforcement volume fraction was 30%, Al reacted with SiO at a temperature of around 950 K to form α-AlO and Si, and the corresponding apparent activation energy was 235 kJ mol. The apparent activation energy of the reaction decreases with the increase of the reinforcement volume fraction. On the other hand, with increasing heating rate, the reaction time was reduced and the characteristic exothermic peak shifted to a higher temperature. The tensile strength and elongation of the composite having the reinforcement volume fraction of 30% were 165 MPa and 3.95%, respectively. On the tensile fracture surfaces, there were many fine dimples in addition to some fractured blocks. The α-AlO particles were located in the center of the fine dimples. The Si crystal blocks fractured along certain cleavage plane in a brittle manner and are a limiting factor to the tensile property of the newly-developed composite. Therefore, the elimination or replacement of the Si crystals by a tougher phase is an important consideration for future work