Characterization of graphite-aluminium composites using analytical electron microscopy

Exposure of graphite fibre/aluminium composites to elevated temperatures, such as those used for processing, can lead to degradation of the mechanical properties. Analytical electron microscopy has been used to examine the phases formed during the heat treatment of the following materials: (a) wire tows of AA6061 aluminium, reinforced with TiBx-coated fibres, and (b) bulk composites produced by hot pressing the tows within a cladding of AA6061. In the tow material, relatively little interaction between the fibres and matrix was observed. Precipitation at the fibre/matrix interface was considerably more advanced in the as-processed bulk composite. Heat-treating both materials at temperatures in the range 580–700 °C resulted in increasingly severe interfacial reactions. Generally, the microstructures at the fibre/matrix interfaces were considerably more complex than reported in previous work. The following phases have been identified following processing or heat-treatment: Al4C3, α′FeSiAl, magnesium spinel, elemental silicon, TiAl3, MgO, βFeSiAl and a “quarternary phase”, MgSiAl(NiCu), together with amorphous oxides and porosity.