The dispersoid evolution, recrystallization and mechanical properties of an Al–Mg–Sc alloy under various homogenization and annealing processes

Abstract

The evolution of Al₃(Sc, Zr) and α-Al(Fe, Mn)Si dispersoids and their influence on the recrystallization behavior and mechanical properties of an Al–Mg–Sc alloy under various homogenization and annealing treatments were investigated by scanning electron microscopy, transmission electron microscopy and tensile testing. The results revealed that the one-step homogenization (OS, 350 °C/6 h) produces higher number density of Al₃(Sc, Zr) and α-Al(Fe,Mn)Si dispersoids compared with the three-stage homogenized alloy (THS8, 270 °C/6 h + 350 °C/6 h + 500 °C/8 h), significantly increasing the recrystallization resistance. The one-step homogenization produces evidently higher strength but lower elongation compared to the there-step homogenization when annealing at low temperature (350 ℃/1 h). However, when annealing at 550 °C/1 h, the one-step and three-step homogenized samples exhibit similar strength, suggesting the mechanical property difference can be eliminated by high temperature annealing. The evolution of Al₃(Sc, Zr) dispersoids during homogenization and annealing treatment plays a key role in determining the property differences of these samples. Although the OS and THS8 treatments produces distinct distributions of Al₃(Sc, Zr) dispersoids, the dispersoids can rapidly coarsen and produce similar dispersoid distributions after annealing at high temperature (550 °C), this difference can only be retained at low temperature annealing (350 °C). Besides, dislocation strengthening is also responsible for the property difference of these alloys. These results provide new information for designing new heat treatment process of Al–Mg–Sc–Zr alloys.