The formation and thermostability of MgO and MgAl2O4 nanoparticles in oxidized SiC particle-reinforced Al-Mg composites

Interfacial reactions and their products in oxidized SiC particle-reinforce d Al-Mg matrix composites were investigated using X-ray diffraction and Fie ld EmissionScanning Electron Microscopy (FE-SEM). Observation of the interf acial reaction between oxidized SiC particles and aluminum alloys containin g Mg showed that nanoparticles of MgO form initially and do not change form when more than 4 wt. % Mg is in the matrix. However, MgO transforms into o ctahedral MgAl2O4 crystals when less than 2 wt. % Mg is in the matrix. Comp arison of the amounts and the sizes of the reaction products MgAl2O4 and Mg O between the Al-Mg alloys with different matrix compositions shows that fe wer MgAl2O4 crystals form at the surface of the particles in the 2014Al mat rix composite than in the Al-2 wt. % Mg (Al-2Mg) matrix composite. Also, th e size of MgAl2O4 in the former composite is greater than that of the latte r composite under the same conditions. However, the amount and the size of MgO crystals that form in the Al-4 wt. % Mg (Al-4Mg) matrix composite is al most the same as that of the Al-8 wt. % Mg (Al-8Mg) composite, and the size of MgO changes a little during heat-treatment at elevated temperatures. Th e amount of the reaction product (either MgO or MgAl2O4) depends on nucleat ion rates and density of nucleation sites on the oxidized SiC particles at the initial reaction. The more completely the nuclei cover the surface of t he oxidized SiC particles, the smaller the resulting size. According to the results, an addition of Mg into the matrix can be used to control the inte rfacial characteristics in the oxidized SiC/Al composites.