Microstructural effects on the spall failure of 7085 aluminum alloy

Abstract

Designing aluminum alloys for spall resistance requires an understanding of the active failure mechanisms under dynamic loading. However, it is time-consuming and expensive to obtain sufficient data to investigate these mechanisms from conventional plate impact spall experiments. Here we use a high-throughput laser-driven micro-flyer plate impact technique to connect the spall failure of aluminum alloy Al7085-T711 to its microstructure. By conducting tests at four impact velocities, we observe the full range of behaviors from incipient spall to complete spall failure. The spall strength of Al7085-T711 increases with both increasing strain rate and peak shock stress, as is typically the case in aluminum alloys. Examination of recovered samples indicates that incipient spall voids initiate primarily at Al7Cu2Fe second-phase particles. To further explore the effect of microstructure on spall failure, we annealed some specimens at 500°C to increase the aluminum grain size while retaining the Al7Cu2Fe particles, which had only a minor effect on spall strength. Solutionizing at 600°C to eliminate the Al7Cu2Fe second-phase particles, on the other hand, increases the spall strength significantly. Our results suggest that spall failure of Al7085-T711 is dominated by the presence Al7Cu2Fe second-phase particles, and that eliminating these particles could result in improved spall resistance of commercial alloys.