Reaction mechanisms, microstructures and tensile properties of the aluminum matrix composites made from Al-SiO2-Mg system were investigated. When the temperature increased from room temperature to around 761 K, Mg dissolved into Al to form Mg-Al alloy. As the temperature increased to about 850 K, the remaining Mg reacted with SiO2 to form MgO, Mg2Si and Si as expressed in step reaction I: 6Mg + 2SiO(2) -> 4MgO + Mg2Si + Si. Finally, with a further increase in temperature, the remaining SiO2 reacted with Al to produce Al2O3 and Si, while MgO reacted with Al2O3 to form MgAl2O4 as expressed in step reaction II: 4Al + 3SiO(2) + 2MgO -> 2MgAl(2)O(4) + 3Si. The Si also dissolved into matrix Al to form Al-Si alloy. Accordingly, its reaction process consisted of two steps and their apparent activation energies were 218 kJ/mol and 192 kJ/mol, respectively. As compared to the composites prepared by Al-SiO2 system, its density increased from 2.4 to 2.6 g/cm(3), and its tensile strength and elongation increased from 165 MPa and 3.95% to 187 MPa and 7.18%, respectively. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.