Evaluation of aluminium-copper alloy reinforced with pitch-based carbon fibres

Abstract

Liquid metal infiltration has been used to make a composite plate consisting of unidirectional pitch-based carbon fibres in aluminium-5 wt% copper alloy. The composite was well consolidated with no discernible carbide formation at the fibre/matrix interface. The large strains generated by differential contraction between fibre and matrix resulted in a high density of matrix dislocations and the development of appreciable residual stress. The slope of the stress/strain curve of the composite was consistent with a longitudinal modulus of 200 GPa, a value significantly lower than that predicted (240 GPa) by the rule of mixtures (ROM). After heat treatment, the composite modulus obtained from stress/strain data was 240 GPa. Now the matrix contained a fine distribution of θ′ precipitates but there were few dislocations present. The tensile strength of the composite was reduced by heat treatment from 420 to 350 MPa and this was attributed to quenching damage to fibres. Transverse properties of the composite were relatively low owing to the inherently low radial properties of the fibre, with a modulus of 30 GPa, in close agreement with the ROM prediction, and a strength of about 50 MPa.