Nanoscale icosahedral quasicrystal phase precipitation mechanism during annealing for Mg–Zn–Gd-based alloys

• Partition distribution of precipitates was attributed to the composition segregation.
• Precipitation of nanoscale I-phase related to solid solution content during annealing.
• The precipitation of nanoscale I-phase meets the nucleation and growth mechanism.

We have performed a systematic transmission electron microscopy study of precipitated particles in Mg–Zn–Gd-based alloys after annealing. We find that the Mg–Zn phases and ellipsoidal-shaped icosahedral quasicrystal phases (I-phase) are precipitated and distributed by partition in the grains, which can be attributed to the composition segregation of the alloying elements in the as-cast alloys. The content of alloying element is found to be crucial to the precipitation of nanoscale I-phase. The nanoscale I-phase ranges in size from a few to dozens of nanometers, revealing that the precipitation process satisfies the classical nucleation and growth theory.