EFFECT OF STRAIN RATE ON DEFORMATIONAL INSTABILITY OF ALUMINUM ALLOYS

Aluminum alloys in a solid solution initial state possess strain-induced structural instability which can be evaluated quantitatively by strain-rate measurements. On account of the intense interactions of clusters with dislocations at small strains (0.2% ε), the K values (σ=σ0+K log ε ̇) for most aluminum alloys are high (K = 16 for an Al-4% Cu alloy at ε=0.2%). However, K decreases significantly with increase in strain and at high strain values (10-15%) K reaches 0.5, a value typical of high purity aluminum (99.999%) at the same degree of strain. Different initial structural states of an aluminum alloy (such as solid solution, GP I and GP II zones of an Al-4% Cu alloy) produce different intensities of interaction of configurations with dislocations and subsequently yield different magnitudes of K at small strains (0.2% ε). As the degree of strain increases, equivalent barrier structures are produced at a critical degree of strain and equivalent K values are then obtained in the various initial state materials. The overall change of K with strain along with the magnitude of dK/dε for any strain increment can be used to ascertain the degree of strain-induced structural instability possessed by a particular aluminum alloy. © 1969.