Effect of annealing on microstructure and mechanical properties of an Al–Mg-Sc-Zr alloy

Understanding the microstructural stability and mechanical response of Al–Mg-Sc-Zr alloys at high temperatures is significant to broaden their aerospace applications. In this study, the effect of annealing temperatures (300, 500, 550 °C) and durations (1, 24, 72 h) on the recrystallization behavior, precipitate evolution and mechanical properties of an Al-6.15Mg-0.3Sc-0.15Zr alloy was investigated comprehensively. Results showed when the annealing temperature was low (<500 °C), the movement of dislocation and the migration of grain/sub-grain boundaries was hindered by precipitates. As the annealing temperature reached 500 °C, the hindering effect diminished due to the coarsening of precipitates. The size of Al₃(Sc,Zr) precipitates increased apparently when annealed at 550 °C for 72 h. Meanwhile, recrystallization occurred due to the diminishing of precipitates hindering. The texture of recrystallized grains was strongly related to the size and density of the Al₃(Sc,Zr) precipitates. In additional, the strength of the material decreased with increasing the annealing temperature and duration. This material softening phenomenon was analyzed statistically. Results indicated that the strength drop at 500 °C was mainly due to the coarsening of precipitates and the decrease of dislocation density, while the sharp strength decrease at 550 °C was also attributed to the coarsening of grains.