Abstract:The Al-Al 2 O 3 -MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M 1 , M 2 , and M 3 , respectively, were prepared at 1700°C for 5 h under a flowing N 2 atmosphere using the reaction sintering method. After sintering, the Al-Al 2 O 3 -MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M 1 was composed of MgO and MgAl 2 O 4 . Compared with specimen M 1 , specimens M 2 and M 3 possessed MgAlON, and its production increased with increasing aluminum addition. Under an N 2 atmosphere, MgO, Al 2 O 3 , and Al in the matrix of specimens M 2 and M 3 reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al 2 O 3 -MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N 2 atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al 2 O 3 -MgO composites were soaked at 580°C for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al 2 O 3 diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al 2 O 3 to form MgAl 2 O 4 . When the temperature was greater than (1640 ± 10)°C, AlN diffused into Al 2 O 3 and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl 2 O 4 at high temperatures because of their similar spinel structures.