Fibre-matrix interactions during fabrication of Al 2O 3Mg metal matrix composites

Abstract

The reactions between alumina fibres and magnesium matrix in metal matrix composites at 1000 K are investigated theoretically and experimentally. The diffusivities of aluminium in layers of spinel and magnesia are estimated and found to be exceedingly low. It is thus concluded that diffusional growth of such layers in the boundary between matrix and fibres will not occur during the casting of the composite. The reaction between amorphous SiO 2 binder and magnesium is further discussed and it is concluded that this may proceed at a considerable rate. Composites cast by means of liquid infiltration are studied metallographically by optical microscopy, scanning electron microscopy and transmission electron microscopy/scanning transmission electron microscopy equipped for microanalysis. The observations are in general agreement with the theoretical results, indicating that the reaction between binder and liquid magnesium is the only important one during fabrication of the composite. It is found that the binder transforms almost completely to a very-fine-grained magnesia and that silicon is dissolved in the molten matrix and precipitated as Mg 2Si upon cooling.