Although the amount of Cr in chemical composition of 7xxx series alloys is usually less than 0.1 wt%, it significantly affects the properties and microstructural evolutions during thermo-mechanical processing of these alloys. In this study, the effect of the elimination of Cr on the microstructural evolutions of ECO-7175 alloy during hot deformation is investigated. ECO-7175 alloys with and without Cr were subjected to hot compression at 350, 400, 450, and 500 °C and strain rates of 0.001, 0.01, 0.1, and 1 s−1. The microstructural evolutions of the alloys were studied through Optical Microscopy, Scanning Electron Microscopy, Scanning Transmission Electron Microscopy, and Electron Backscatter Diffraction analysis. Scanning Electron Microscope and Scanning Transmission Electron Microscope observations revealed that removal of Cr eliminates ε precipitates from microstructure of the alloy. The elimination of ε precipitates that act as Zener pining agents were found to affect the kinetics of static recrystallization of the initial materials during the preheating and mechanisms of dynamic restoration of the alloy during hot deformation. Although the microstructural observations revealed that continuous dynamic recrystallization and dynamic recovery were the main restoration mechanisms for both alloys, Electron Backscatter Diffraction analysis showed that the finely dispersed ε precipitates impede movement and rearrangement of dislocations and slow down the rate of dynamic recovery and continuous dynamic recrystallization in the Cr-containing samples.
