An experimental study of shear localization in aluminum-copper single crystals

Abstract

Localized plastic shearing was studied in single crystals of Al-2.8 wt% Cu single crystals aged to contain GP zones, θ′ and θ precipitates. For θ′ containing crystals, the onset of macroscopic shear localization corresponded to the attainment of a critically low value of the ratio of slip plane strainhardening rate, ft, to current tensile stress σ, (h/'σ) crit. The average value of (h/σ) crit was 0.032 in close agreement with our recent theoretical models. The bands were not aligned with the active slip systems in the crystal's matrix but were misaligned by several degrees. This misalignment is shown, theoretically and experimentally, to lead to ‘local geometrical softening’ in the bands. Crystals containing GP zones also developed macroscopically localized shear bands corresponding to the above critical conditions and with the same kinematical features, but macroscopic shearing was usually preceded by the formation of coarse bands of slip. These coarse slip bands were aligned with the active slip systems and we found that their beginnings could be correlated with a critically low value of the ratio of ( h/ G) ≈ 2 × 10 −3, where G is the elastic shear modulus. Strainsoftening, i.e. h < 0, was not observed under any conditions, even after the shear bands had accumulated large amounts of shear strain.