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 degrees C-490 degrees 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.