Synthesis and characterization of in situ (Al₂O₃-Si)/Al composites by reaction hot pressing

In situ (Al₂O₃-Si)/Al composites with a reinforcement volume fraction of 10% were synthesized from the Al-SiO₂ system using low energy ball milling and reaction hot pressing. Differential thermal analysis was used to investigate the reaction mechanisms between SiO₂ and Al. X-ray diffraction results revealed that the reaction between Al and SiO₂ took place completely at 900°C with a holding time of 2 h, thereby forming Al₂O₃ and Si. Scanning electron microscopic, energy dispersive X-ray spectroscopic, and transmission electron microscopic (TEM) results showed that the in situ synthesized Al₂O₃ and Si particles, whose sizes are less than 2 μm, were polygonal in shape and dispersed uniformly in the matrix. Moreover, Al₂O₃ particle size showed a tendency to increase from ∼2 to ∼6 μm when the synthesis temperature was increased. Furthermore, TEM observation showed that the interface between the reinforcements and Al matrix is clean. The yield strength, ultimate tensile strength, and Brinell hardness of the in situ (Al₂O₃-Si)/Al composite was significantly higher than the aluminum matrix. Mechanisms governing the tensile fracture process are discussed.