Reaction mechanisms, resultant microstructures and tensile properties of Al-based composites fabricated in situ from Al-SiO2-Mg system

•Composites (MgAl2O4 + Mg2Si + Si)/Al can be in situ fabricated from Al-SiO2-Mg system.•The Mg can eliminate the big block Si and improve the properties of the composites.•The reaction process of the Al-SiO2-Mg system can be divided to two intermediate steps.•The two intermediate reactions corresponded apparent activation energies are 218 and 192 kJ/mol.•The tensile strength and ductility of the composites are 187 MPa and 7.18%, respectively.

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 + 2SiO2 → 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 + 3SiO2 + 2MgO → 2MgAl2O4 + 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/cm3, and its tensile strength and elongation increased from 165 MPa and 3.95% to 187 MPa and 7.18%, respectively.

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