Thermal stability of microstructure and texture in an ultra-fine grained (UFG) Al–Mg–Sc–Zr alloy

The present investigation is aimed at exploring the microstructural stability of the ultra-fine grain (UFG) non-heat treatable Al-alloy AA5024 (Al–Mg–Sc–Zr), containing thermally stable and coherent Al₃(Sc_x, Zr_1-x) precipitates. The alloy has been purposefully given severe rolling reductions of 90%, 95% and 98% in uni-directional (UDR) and cross-directional (CR) rolling and was subsequently annealed at 350°C starting from 1 to 100 h to assess the role of the defect-populated microstructure and crystallographic texture on the stability of this alloy. An interesting observation has been made that recovery is prevalent, with very slow kinetics, which has been attributed to the stability of the precipitates during annealing. The crystallographic texture is Cu type (a typical high SFE alloy) that remains identical for annealed and deformed states for both UDR and CR sheets. However, a decrease in orientation distribution function (ODF) strength has been observed at 98% of UDR, whereas this decrease comes at 95% in the CR case. These findings indicate the possibility for intermittent dynamic recovery just before these reduction levels and a slight increase in the fraction of recrystallised grains. A comparison of texture obtained from the visco-plastic self-consistent crystal plasticity (VPSC) simulation with the experimental texture clearly showed the contribution of recrystallisation in overall texture that caused a drop in texture intensity.