In this research in-situ aluminum matrix composites were synthesized through pyrolysis of TEOS in the melt. For this purpose 0.5, 1, 2 and 3 wt.% of cross linked TEOS were gradually added to melt at 850°C and stirred for 20- 30 minutes then the melt temperature reduced fastly to 730 °C and stirred for 5 minutes. Consequently reinforcement particles, a compound of Si, C, N and O, were formed and dispersed in melt. The slurry were solidified in a cylindrical permanent mold. Structural examinations demonstrated uniform dispersion of reinforcement particles in the matrix. Mechanical test results indicated that hardness, yield and ultimate tensile strengths were markedly increased. An important achievement of using this aluminum matrix composite synthesis method was small elongation loss, in comparison with the conventional composites manufacturing methods. In the optimum sample, enhancement of 53% in yield strength and about 21% in ultimate tensile strength were achieved in cost of only 19% elongation decrease in comparison to the monolithic sample. The bending and shear strength were also enhanced 43% and 21%, respectively. Keywords: Cast composite, Reinforcement, Particles, Cross-linking, Pyrolysis, Aluminum matrix, Mechanical properties.
