Hot deformation behavior of in-situ nanosized TiB₂ particulate reinforced AZ91 Mg matrix composite

In this study, hot deformation behavior of in-situ nanosized TiB₂/AZ91 composite is investigated by analyzing the constitutive equation, hot processing maps and microstructure evolutions. Hot compression tests are conducted in different temperatures and strain rates range of 523–673 K and 0.001–1 s⁻¹ with a constant strain of 0.69. The results show that deformation temperatures and strain rates have a strong influence on the flow behavior of the composite, exhibiting typical work hardening, softening and steady stages. The constitutive equation is established through determining material constants, which can predict the flow stress precisely. In the meanwhile, the stress exponent (n)is calculated as 5.4, suggesting the hot deformation mechanism of TiB₂/AZ91 composite is dominated by the dislocation climb. And the calculated apparent activation energy (Q)is 168.8 kJ/mol, which is higher than that of unreinforced AZ91 alloy due to the addition of nanosized TiB₂ particles. Furthermore, the hot processing maps of TiB₂/AZ91 composite are developed based on dynamic materials model, presenting three domains: one instability region in the range of 523–623 K & 0.01–1 s⁻¹, and two safe regions in the range of 548–600 K & 0.001–0.005 s⁻¹ and 648–673 K & 0.1–1.0 s⁻¹ with the peak efficiency value of 0.36, respectively. By observing microstructures, full dynamic recrystallization (DRX)occurs in the safe regions, while the mechanism of instability region is dominated by mechanical twining and high density dislocation.