Influences of carbon additions on reaction mechanisms and tensile properties of Al-based composites synthesized in-situ by Al–SiO2 powder system

The effects of carbon additions on reaction mechanisms and mechanical properties of Al-based composites fabricated in-situ through Al–SiO2 system were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). It was found that when the powder of C was added into the Al–SiO2 system, Al first reacted with SiO2 to form the α-Al2O3 and Si. Some of the Si then reacted with the C to form the SiC, and the remaining Si dissolved into Al to form the Al–Si alloy. Based on the DSC curves obtained from five different heating rates, the apparent activation energy for the synthesis of the new composites was calculated and found to be 309 kJ/mol, which was larger than that of Al–SiO2 system that yielded the same reinforcement volume fraction of 30%. As compared with the reference materials prepared from the Al–SiO2 system, the morphology of Si in the new composites changed from a large block to a needle-like shape. Moreover, the tensile strength and ductility of the new materials increased from 165 MPa and 3.95% to 208 MPa and 4.20%, respectively.