The tensile deformation and fracture characteristics of some aluminium alloys

Abstract

It was required to determine the true stress/true strain behaviour of several alloys, and to relate this behaviour to their fracture characteristics. A device was produced which measured the change in diameter of a tensile specimen during testing. The onset of necking was sensitively detected, and the gauge length minimum diameter measured at intervals up to within 3–5 sec of fracture. True transverse strain was then obtained together with corrected stress. Curves for a number of materials and conditions are given in the paper (naturally and artificially aged Al-Cu-Mg alloys and Al-Zn-Mg-Cu alloy). The necking strains, fracture strains, and strain hardening indices are discussed and the difference in strain hardening of naturally and artificially aged Al-Cu-Mg alloys is shown in terms of these parameters. The differences between commercial duralumin and a super pure ternary compositon are also shown. Metallographie evidence of the sequence of particle cracking and formation of voids up to the point of fracture is also presented in the paper. The effects of such features in commercial alloys, together with grain boundary weakness in the super pure composition are considered.