Effect of alumina coating and extrusion deformation on microstructures and thermal properties of short carbon fibre–Al composites

Short carbon fibres were coated with alumina by sol–gel process. Uncoated and alumina-coated short carbon fibre–Al composites were fabricated by gas pressure infiltration process. The effects of alumina coating and extrusion deformation on microstructures and thermal properties of the composites were studied. The results show that alumina coating is effective to improve the quality of the short carbon fibre preform as well as act as diffusion barrier to impede interfacial harmful chemical reactions between aluminium and short carbon fibres, which would increase the thermal properties of the composites. Extrusion deformation can orient the carbon fibres to the extrusion direction to improve their degree of orientation, meanwhile decreasing their aspect ratio. Extrusion deformation has a beneficial effect on the thermal conductivity of the composites. However, its effect on coefficient of thermal expansion of the composites is small because the effects of the improvement in degree of orientation and the decrease of aspect ratio tend to cancel each other somewhat.