Temperature-Dependent Role of LPSO Phases in Particle-Stimulated Nucleation of Dynamic Recrystallization in Mg Alloys

Particle-stimulated nucleation (PSN) of dynamic recrystallization (DRX) is generally attributed to the accumulation of interfacial defects arising from plastic deformation incompatibility between a second phase and the surrounding matrix. When the second phase is highly deformable, however, reduced plastic strain mismatch may diminish the PSN effect. In this study, the influence of the long-period stacking ordered (LPSO) phase on DRX behavior in Mg alloys is quantitatively examined using hot-compression experiments over a range of temperatures. A statistical comparison between LPSO-containing and LPSO-free alloys reveals that the LPSO phase has a negligible effect on DRX at 400 °C, but significantly promotes DRX at 500 °C. By integrating diffraction-pattern preprocessing with full-pattern-matching spherical indexing, reliable phase- and grain-resolved orientation and strain analyses of both DRX grains and LPSO phases are achieved. At 400 °C, the LPSO phase deforms cooperatively with the Mg matrix owing to their comparable strengths, resulting in limited interphase strain mismatch and weak PSN activity. In contrast, at 500 °C, more rapid softening of the Mg matrix leads to reduced deformation of the LPSO phase, intensifying interphase strain incompatibility and thereby enhancing PSN-driven DRX. Additionally, LPSO grains accommodate deformation through grain-boundary dissociation at 500 °C, increasing particle number density and LPSO/Mg interfacial area, which further promotes DRX nucleation while suppressing grain coarsening. These findings elucidate the temperature-dependent role of deformable second phases in PSN-controlled DRX and provide guidance for designing thermomechanical processing routes and microstructures for improved Mg alloy performance.