A study of the mechanical properties and microstructure of fibre-reinforced aluminium alloy

Abstract

A well-consolidated composite, consisting of aluminium-magnesium-silicon alloy (6061) and continuous alumina-based fibres, has been fabricated 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 in the matrix to allow precipitation-hardening upon heat treatment. The bond between fibre and matrix is strong, as evidenced by the mechanical properties, which match ‘rule of mixtures’ predictions with a longitudinal Young’s modulus of ~ 130 GPa and transverse value of ~100 GPa. The shear modulus, ~ 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 discussed. Composite yield stress differs in longitudinal and transverse directions (55 MPa and 70 MPa, respectively) due to anisotropic residual stresses in the matrix. Strength in the longitudinal direction is 245 MPa, indicative that fibre strength is reduced during composite manufacture, while transverse strength matches that of unreinforced alloy (170 MPa), as expected with a strong fibre-matrix bond. Heat treatment to matrix peak-hardness increases yield stress and strength but leads to some reduction in ductility.