A STUDY OF THE MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF FIBER-REINFORCED ALUMINUM-ALLOY

A well-consolidated composite, consisting of aluminium-magnesium-silic on alloy (6061) and continuous alumina-based fibres, has been fabricat ed by liquid metal infiltration. No deleterious reaction products were formed at the fibre-matrix interface and, although a small amount of magnesium penetrated outer regions of the fibre, sufficient remained i n the matrix to allow precipitation-hardening upon heat treatment. The bond between fibre and matrix is strong, as evidenced by the mechanic al properties, which match 'rule of mixtures' predictions with a longi tudinal Young's modulus of similar to 130 GPa and transverse value of similar to 100 GPa. The shear modulus, similar to 25 GPa, is the same as unreinforced alloy, showing that shear is controlled essentially by the matrix. The effect of fibre orientation on Poisson's ratio is dis cussed. Composite yield stress differs in longitudinal and transverse directions (55 MPa and 70 MPa, respectively) due to anisotropic residu al stresses in the matrix. Strength in the longitudinal direction is 2 45 MPa, indicative that fibre strength is reduced during composite man ufacture, while transverse strength matches that of unreinforced alloy (170 MPa), as expected with a strong fibre-matrix bond. Heat treatmen t to matrix peak-hardness increases yield stress and strength but lead s to some reduction in ductility.