Formation of aluminum/alumina ceramic matrix composite by oxidizing an Al–Si–Mg alloy

In the formation of an Al–Al2O3 ceramic matrix composite by oxidizing an Al–Si–Mg alloy, it was found from electron microscopy that MgO appeared first on the surface of the sample and followed by the formation of MgAl2O4 spinel. This order of appearance could be postulated by considering the high partial pressure of Mg and the Gibbs free energy associated with each reaction during annealing. The MgO inhibited the oxidation of molten Al underneath and preserved the Al metal inclusions, while spinel allowed oxygen to diffuse into the Al alloy so that Al was oxidized to form the Al2O3 ceramic matrix.