Non-quadratic and asymmetric yield locus evolution of AA2219-T87 aluminum alloy under in-plane biaxial loading

Uniaxial and planar biaxial tests for AA2219-T87 alloy were carried out using a modified in-house developed design of cruciform specimens, and the yield behaviour was investigated for all four quadrants of the stress space. The alloy exhibited a pronounced dependence of the yield behaviour on the stress state. For the uniaxial tests, higher yield stress was observed in compression than in tension. The opposite trend was observed for the biaxial tests, where the biaxial tension showed higher yield stress in comparison to the biaxial compression. Different yield criteria were used to capture the experimental yield loci, and the Yld2000 criterion captured the experimental data with the most accuracy. Moreover, the incremental plastic strain direction was closely aligned with the Yld2000 predicted normal across different load ratios. The strain hardening behaviour was also analysed under uniaxial and biaxial loading conditions. It was found that the strain hardening was significantly increased under the biaxial loading, which was further confirmed by the work hardening analysis and a detailed study of the microstructure and texture evolution. The fractography study further revealed a transition from ductile fracture with voids and dimples under uniaxial loading to ductile-brittle mixed mode with prominent facet formation under biaxial loading.