Difference in the Hot Compressive Behavior and Processing Maps between the As-cast and Homogenized Al-Zn-Mg-Cu (7075) Alloys

The deformation mechanisms and processing maps of the as-cast Al-Zn-Mg-Cu (7075) aluminum (Al) alloy were studied and compared with those of the homogenized 7075 Al alloy in the temperature range of 573-723 K and in the strain rate range of 10−3-10 s−1 to explore a possibility for directly using the as-cast 7075 Al alloy as a billet for hot working. The as-cast and homogenized 7075 Al alloys had similar grain sizes and showed similar high-temperature deformation behaviors. The as-cast 7075 Al alloy, however, exhibited higher power efficiencies and smaller unstable flow regions compared to the homogenized 7075 Al alloy because of the presence of secondary phases (MgZn2) segregated at the dendritic interfaces in the as-cast microstructure, which were formed during non-equilibrium solidification. These segregated phases provided nucleation sites for dynamic recovery or continuous dynamic recrystallization, and as a result a fine and more homogeneous (sub)grain structure could be obtained from the as-cast microstructure compared to the homogenized microstructure. The current work suggested the possibility and advantage of using as-cast microstructures for hot working of aluminum alloys with high content of solutes.