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 a lloys during fabrication by compocasting and subsequent remelting at 8 00 degrees C for 30 minutes have been studied using analytical transmi ssion electron microscopy (TEM) and scanning electron microscopy (SEM) . Experimental results show that MgO is the main reaction compound pro duced by the reaction 3Mg (1) + Al2O3 (s) = 3MgO (s) + 2Al (1). The Mg O crystals formed by interfacial reaction are very small (about 5 to 2 0 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 reacti on kinetics is controlled by seepage of Mg and release of Al (1) along the newly formed MgAl2O4 or MgO grain boundaries. Because of the larg e volume expansion during the formation of MgO from the reaction betwe en Mg (1) and Al2O3 and because of the low diffusivity in MgO crystal, the reaction rate is very low.