Effect of Strain Rate on the Microstructure and Mechanical Properties of AA2B06-O Aluminum Alloy of the Al–Cu–Mg System

The mechanical properties in the tension and microstructure of aviation aluminum alloy AA2B06-O (the Al–Cu–Mg system) at low (10–3–1 s–1) and high (1293–5045 s–1) strain rates are studied. At relatively slow (quasistatic) tension, the stain rate has a small effect on the mechanical properties. Upon fast (dynamic) loading, a raising strain rate results in a substantial, by a factor of about 2, simultaneous increase in the ultimate tensile strength of the alloy and its plasticity (elongation to failure), whereas the yield stress remains almost unchanged. Transmission electron microscopy has revealed a homogeneous nature of plastic deformation on the microlevel upon slow loading and an inhomogeneous one upon fast loading. The latter reveals itself in the localization of deformation in the form of adiabatic microshear bands where complex dislocation structures are formed, such as dislocation tangles and dipole and multipole configurations. In certain domains of microshear bands, the first stage of dynamic recrystallization is observed because of the heat release of localized plastic deformation. It is shown that the changeover of deformation mechanisms when passing from quasistatic to dynamic tension is responsible for the drastic change in mechanical behavior of the material. Thus, a simultaneous increase in both strength and plasticity can take place not only in nanostructured materials obtained by severe plastic deformation techniques, e.g., equal channel angular extrusion, but also upon high strain rate deformation of an aluminum alloy having an ordinary microstructure after rolling and low-temperature annealing. The experimental results open up new prospects for the practical application of methods of high strain rate pulse deformation, such as impact hydroforming, for producing complexly shaped articles made out of sheet blanks by a single operation due to the substantially improved technological plasticity of the material.