ON THE FORMATION OF AL2O3-AL COMPOSITE BY DIRECTED OXIDATION OF MOLTEN METALS

The formation process of Al2O3-Al composite by directed oxidation of m olten Al alloys (so-called Lanxide process) was studied mainly by scan ning electron microscopy. Emphasis has been put on the effect of SiO2 powders used as external dopants on the incubation period of the Lanxi de process. It was observed that doping SiO2 powder on the top of the Al alloy can decrease the incubation time substantially, by retarding the reaction Mg2+ + O2 --> MgO and promoting the reaction MgO+Al3+ +O2 --> MgAl2O4, which makes it much easier for Al microchannels reach to the free surface to start the bulk oxidation of Al-->Al2O3. In additi on, such an oxidation reaction becomes predictable and controllable.