Process, microstructure and properties of squeeze-cast short-carbon-fibre-reinforced aluminium-matrix composites

Two types of high-modulus short-carbon-fibre-reinforced commercially pure aluminium-matrix composites were fabricated in-house using a home-made squeeze caster. The type-I composites were fabricated from short-fibre preforms in which fibres exist as dispersed bundles. The type-II composites were fabricated from preforms in which individual fibres were uniformly dispersed. The detailed processes are described in the text. A three-point-bending strength of higher than 200 M Pa was obtained for the type-1 composite with 17 vol% of fibre. When more fibre was incorporated, both the strength and the ductility decreased due to inadequate infiltration. However, a bending strength of greater than 240 MPa was recorded on a hot-rolled type-I composite with a fibre content as high as 28 vol%. This significant improvement in the mechanical properties is explained by a hot-rolling-induced void-healing effect. The type-II composites, with lower fibre volume fractions than those of the type-I due to their different preforms, exhibited bending strengths up to 166 MPa. Scanning electron microscopy fractography shows that the two types of composites fracture in distinctive manners. Transmission electron microscopy results featured thermal-stress-induced dislocations at carbon-aluminium interfaces as well as submicrometre-sized aluminium carbide, the reaction product, which nucleated from the interface and grew into the matrix interior.