Effect of TiB₂ particles on dynamic recrystallization in TiB₂-reinforced Al–Zn–Mg–Cu–Zr during hot compression

We investigated the microstructure evolution of a 6 wt% TiB₂-reinforced Al–Zn–Mg–Cu–Zr composite subjected to hot compression at temperatures within the range 370 °C–490 °C, at strain rates between 0.001 s⁻¹ and 10 s⁻¹. The microstructure evolution was characterized by electron backscatter diffraction and transmission electron microscopy. Dynamic recovery and dynamic recrystallization mechanisms were analyzed, with a focus on nucleation at original grain boundaries and TiB₂ particles. The results show that recovery is the main dynamic softening mechanism due to the high dislocation mobility in the Al matrix. However, low temperature and high strain rate results in a large number of small recrystallized grains, whereas high temperature and low strain rate results in a few large recrystallized grains. Dynamic recrystallization is mainly attributed to particle-stimulated nucleation occurring near TiB₂ particles/clusters, especially TiB₂ particles/clusters at grain boundaries. Relations between the observed dynamic recrystallization and the Zener-Hollomon parameter are discussed.