Quasi-static and dynamic response of AA-2219-T87 aluminium alloy

Abstract

Quasi-static and high-strain rate uniaxial compression testing on AA-2219-T87 aluminium alloy were carried out under varying strain rates (ranging from 1×10−3 to 7×103 s−1) and temperatures. Quasi-static testing showcased no strain-rate sensitivity (SRS) at room temperature, while positive SRS was observed at elevated temperatures (180, 230, and 300°C), showcasing higher flow stress with an increase in strain rate. This temperature-dependent SRS is attributed to the typical activation of thermally activated processes, greater dynamic recovery, and reduced effectiveness of traditional strengthening mechanisms at higher temperatures. High-strain rate testing, performed using a Split Hopkinson pressure bar (SHPB), revealed no SRS across all tested temperatures (25, 180, and 230°C). At high-strain rates (>103), once the flow stress reaches a common flow stress, it undergoes either a steady state deformation or minor softening. This behaviour is explained by the interplay between strain hardening and thermal softening phenomena. Specifically, the formation of intense shear flow zones (including dynamic recrystallization) during impact loading at strain rates of 4×103 and 7×103 s−1 promoted thermal softening over strain hardening, resulting in flow stress levels similar to those observed at a strain rate of 1×103 s−1. The intense shear flow volume fraction increased with an increase in strain rate, which is linked to no SRS and higher strain at 4×103 s−1 and 7×103 s−1. The SHPB testing data was utilized to develop the constitutive Johnson-Cook model, enabling the determination of the plastic behaviour of the AA-2219-T87 alloy at high-strain rates and temperatures. These findings enhance our understanding of the alloy's mechanical response and provide valuable insights for optimizing its performance in high-strain-rate applications.