OXIDE MATRIX COMPOSITE BY DIRECTIONAL OXIDATION OF A COMMERCIAL ALUMINUM-MAGNESIUM ALLOY

Oxidation rates of a commercial Al-Mg alloy, Al-5083, were investigate d to understand the synthesis of an oxide-based composite. In some exp eriments, the oxide layer was grown with several platinum wires embedd ed in the matrix to facilitate transport of electrons. The oxidation r ate was not controlled by the rate of transport of the electrons and p ositive holes through the ceramic oxide layer. In the initial phase of the composite growth, an incubation period was observed due to format ion of MgO on the alloy surface. At 1273 K or higher, the incubation p eriod was followed by a period of sustained oxidation after MgO was co nverted to a spinel layer. It is demonstrated that, after the initial incubation period, the rate of oxidation is influenced by the rate of transport of ions through the oxide matrix composite.