Stress-accelerated softening in bulk nanocrystalline Mg-Gd-Y-Zr alloys

Exploring the microstructure and mechanical property evolution of metallic structural materials during stress annealing has scientific and engineering significance since these materials are usually used to bear coupled thermo-mechanical loads in their service life. Here, we report a stress-accelerated softening phenomenon in bulk nanocrystalline Mg-Gd-Y-Zr alloys. Transmission electron microscopy observation indicates that, compared with static annealing, stress annealing accelerates the grain coarsening and precipitation of the grain boundary β phases. The precipitation of β phases results in the depletion of intragranular solute atoms, which therefore weakens the solid solution strengthening effect. The stress-assisted β phase precipitation and grain coarsening lead to the accelerated softening of nanocrystalline Mg-Gd-Y-Zr alloys. That is, the mechanical properties of nanocrystalline Mg-Gd-Y-Zr alloys subjected to coupled thermo-mechanical loads deteriorate more rapidly compared with the statically-annealed alloys.