Effects of temper condition on high strain-rate deformation of AA 2017 aluminum alloy in compression

Abstract

Cylindrical specimens of AA 2017 alloy in T451, T651 and O temper conditions were subjected to quasi-static compressive loading at a strain rate of 3.2×10−3 s−1 and dynamic impact loading at strain rates between 3000s−1 and 8000s−1. The effects of strain rates and temper condition on damage evolution were investigated. Deformation under quasi-static loading was dominated by strain hardening while high strain rates deformation was characterized by two-peak stress–strain curves, indicating simultaneous occurrence of hardening and softening controlling deformation. The degree of softening after the first peak is highest in the annealed sample while the age-hardened specimens showed higher degree of softening beyond the second peak. Both deformed and transformed shear bands were observed in the impacted age-hardened specimens, whereas only deformed bands developed in the annealed specimens. The critical strains for the onset of the thermomechanical instability leading to the formation of adiabatic shear bands are about the same for both T451 and T651 specimens, but much higher for the annealed (O) specimens. The age-hardened specimens fractured in a manner consistent with ductile fracture mode that is characterized by the sequential nucleation, growth and coalescence of micro-voids inside transformed shear bands.