Insight into the recrystallization behavior and precipitation reaction of in-situ nano TiB2/AlCuMg composite during heat treatment

Highlights: • Deformed Al around TiB₂ boosts recrystallized behavior during water quenching. • Trace Mg visibly enhances the precipitation kinetics in composite. • The rearrangement of Cu enables to transform θ″ precipitates to θ' precipitates. • Misfit dislocations at TiB₂/Al interface play a vital role on precipitation reactions. In this study, the quantitative results from both electron backscattered diffraction and transmission electron microscope analyses provided the fundamental insight into the recrystallized behavior and precipitation reaction of the in-situ nano TiB₂/AlCuMg composite during heat treatment. The difference of coefficient thermal expansion between TiB₂ particles and Al matrix enabled the formation of deformation zone around TiB₂ clusters during water quenching which promoted the recrystallized behavior. Besides, the strong pinning effect induced by TiB₂ distributed at recrystallized grain boundary was also observed. As a result, the fine recrystallized grains were generally distributed around particle clusters. During artificial aging process, the trace Mg remarkably enhanced the kinetics of precipitation reaction in the composite. The coexistence of θ″ and θ' precipitates confirmed the continuous transformation of θ″ into θ' via the atomic Cu rearrangement. Herein, the θ'/Al interface acted as a heterogeneous nucleation site of the Al₃Zr precipitate was able to improve the nucleation and growth rate of the precipitate. Moreover, the misfit dislocations at TiB₂/Al interface with larger lattice mismatch were confirmed. The synergistic effect of stress field caused by misfit dislocations and geometrically necessary dislocations facilitated the pipe diffusion was responsible for transporting solute atoms under depleted vacancy and solute atoms around the interface, benefited to the nucleation and growth of precipitates.