Effect of current Mg concentration on interfacial reactions during remelting of Al-Mg(5083)/Al2O3p composites

The interfacial reactions between Al2O3 particles and 5083 Al-Mg alloys during fabrication by compocasting and subsequent remelting at 800 degreesC for 0.5 and 4 h have been studied using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It is found that the reaction product is changed with increasing remelting time. MgO is the main reaction product after casting and remelting for 0.5 h. The MgO crystals are then very small (about 5-20 nm in size) and the reaction zone is about 50-80 nm thick for the as-cast material and about 100-150 nm after remelting for 0.5 h. However, after remelting for 4 h, MgO is transformed into MgAl2O4 and the interfacial region is then constituted of large MgAl2O4 crystals of about I pm in size. This transformation indicates that the nature of the reaction products is controlled by the current Mg content in the matrix. (C) 2002 Elsevier Science Inc. All rights reserved.