Deformation of age-hardened aluminium alloy crystals—II. Fracture

Abstract

Single crystals of Al-3.7 wt. % Cu, Al-20 wt. % Ag and Al-15 wt. % Zn, aged to contain GP zones, fracture by shear on a {111} plane in a 〈11̄0〉 direction followed by crack propagation. There are three stages in the fracture. First, coarse slip bands appear at a constant resolved shear stress which depends on temperature for a given material. Secondly, a large shear occurs on one of these and lastly a crack forms at the foot of the shear step produced. The first two stages also appear in compression. The coarse slip bands which initiate fracture appear to be produced at such a shear stress that the stress for their appearance minus the critical resolved shear stress is roughly constant at a given temperature although slightly affected by alloy content. It is concluded that the appearance of the coarse slip bands is a property primarily of the work hardened matrix and not of the precipitates, and that they appear when some barrier formed during work hardening is broken down.