A detailed investigation on the grain structure evolution of AA7005 aluminum alloy during hot deformation

Obtaining a fine grain structure in Al-Zn-Mg-Cu aluminum alloys with a relatively low alloying content, such as AA7003 and AA7005, is required when they are used for vehicle bodies. However, comprehensive studies on these materials are still needed. In this study, the grain refinement capability of the commercially used AA7005 aluminum alloy through a hot deformation process with relatively a low strain level was investigated. Hot compression tests were performed over a wide range of temperatures, strain rates, and strains (300–500 °C, 0.005–50 s−1, and 0.3–1.1, respectively). Diverse types of grain structure evolution, including dynamic recovery (DRV) and dynamic recrystallization (DRX), occurred during the thermomechanical process, and the related mechanisms were analyzed. The results show that DRV occurred regardless of the deformation parameters, while the occurrence of DRX was highly dependent on the parameters. DRX was more favorable at high temperatures, low strain rates, and large strains (e.g., 500 °C, 0.005 s-1, and 1.1, respectively). It formed new high-angle grain boundaries and resulted in fine grains through low-angle grain boundary rotation, high-angle grain boundary migration, and serration mechanisms, which played the primary role in grain refinement. By carefully controlling the deformation parameters, the original coarse grains were successfully refined down from hundreds of micrometers to 8–25 μm. The results indicate that the AA7005 aluminum alloy has a great potential for grain refinement through hot deformation, but special attention should be paid to the parameters.