The strain rate and temperature dependence of the dynamic impact properties of 7075 aluminum alloy

The dynamic impact properties of 7075 aluminum alloy are studied experimentally using a split Hopkinson bar. Cylindrical specimens of 10 mm height and 10 mm diameter are compressed dynamically at temperatures ranging from 25 to 300 degrees C and at constant strain rates of from 10(3) to 5x10(3) s(-1). The influence of strain rate and temperature on the mircrostructural evolution, the fracture mechanisms and the occurrence of shear localization is investigated. It is found that the compressive stress-strain response depends sensitively on the applied strain rate and test temperature. Considering the effects of strain rate, temperature, strain hardening, rate sensitivity and thermal softening of the material, a constitutive equation is used successfully to describe the dynamic impact deformation behavior of 7075 Al alloy. Microstructural observations reveal that the size of the initial coarse equi-axial grains is reduced as the strain rate and temperature increase due to dynamic recrystallization. In contrast, the second phase increases in size in response to increasing strain rate and temperature. SEM observation of the fracture surfaces makes evident an adiabatic shearing mechanism along the fracture planes accompanying crack formation. (C) 2000 Elsevier Science S.A. All rights reserved.