INTERFACIAL REACTIONS IN AL-MG (5083)/AL(2)O(3)P COMPOSITES DURING FABRICATION AND REMELTING

The interface reactions between alpha-Al2O3 particles and 5083 Al-Mg alloys during fabrication by compocasting and subsequent remelting at 800 degrees C for 30 minutes have been studied using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Experimental results show that MgO is the main reaction compound produced by the reaction 3Mg (1) + Al2O3 (s) = 3MgO (s) + 2Al (1). The MgO crystals formed by interfacial reaction are very small (about 5 to 20 nm in diameter), and the reaction zone is about 50 to 80-nm wide for as-cast materials and about 100 to 150 nm after remelting. The reaction kinetics is controlled by seepage of Mg and release of Al (1) along the newly formed MgAl2O4 or MgO grain boundaries. Because of the large volume expansion during the formation of MgO from the reaction between Mg (1) and Al2O3 and because of the low diffusivity in MgO crystal, the reaction rate is very low.