Abstract: Abstract The study on the mechanism of reactive processing for the fabrication of α-Al₂O_3p/Al composite was performed by pressureless metal infiltration technique,optical micrography,SEM-micrography and EDS-analysis and thermodynamic consideration. This suggests the mechanism of reactive processing:the atmosphere of limited volume in vacancies between alundum particles (α-Al₂O_3p)could chemically react with Al-and Mg-element in the molten AlMg10 alloy infiltrated spontaneously into the preform of alundum particles,forming solid phases and a vacuum,i.e.,a driving force for the infiltration;due to the long time contact between the molten AlMg10 alloy and alundum particles and additives,etc.,at elevated temperatures,there might be chemical reactions.