Effect of strain rate on the microstructure and mechanical properties of aluminum alloy AA2B06-O of the Al–Cu–Mg system

The study covers the tensile properties and microstructure of AA₂B06-O aerospace aluminum alloy (Al–Cu–Mg system) at low (0.001–1.0 s–¹) and high (1293–5045 s–¹) strain rates. The stain rate at relatively slow (quasistatic) tension has a small effect on mechanical properties. Rasing strain rate at fast (dynamic) loading results in a substantial (nearly twofold) simultaneous increase in the ultimate tensile strength and plasticity (elongation to failure) of the alloy with the yield stress virtually unchanged. Transmission electron microscopy revealed a homogeneous nature of plastic deformation on the microlevel at slow loading and inhomogeneous one at fast loading. The latter is observed as localized deformation in the form of adiabatic microshear bands where complex dislocation structures are formed such as dislocation tangles, dipole and multipole configurations. The first stage of dynamic recrystallization is observed in certain domains of microshear bands due to the heat released at localized plastic deformation. It was shown that the changeover of deformation mechanisms when passing from the quasistatic to dynamic tension causes a significant 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 pressing), but also at the 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 practical application of high strain rate pulse deformation methods, such as impact hydroforming, for producing complex-shape articles from sheet blanks in one operation due to substantially improved technological plasticity of the material.