Effect of Gd Addition on Hot Deformation Behavior and Microstructure Evolution of 7075 Aluminum Alloy

In order to clarify the effect of rare earth Gd on the microstructure evolution and deformation behavior of 7075 aluminum alloy during hot compression, uniaxial compression tests of Al-Zn-Mg-Cu-0.5%Gd were conducted at strain rates of 0.001, 0.01, 0.1, and 1 s-1 with the temperatures ranging from 350 to 450 degrees C. The microstructural evolution during deformation was characterized using optical microscopy and electron backscatter diffraction (EBSD) techniques. The experimental results indicate that the addition of the rare earth element Gd significantly increases the peak flow stress and thermal activation energy of the alloy. Due to the pinning effect of rare earth phases, dislocation movement is hindered, leading to an increased level of work hardening in the alloy. However, the dynamic recrystallization of the alloy is complicated. At a high Z (Zener-Hollomon parameter) values, recrystallization occurs in the form of DDRX (Discontinuous Dynamic Recrystallization), making it easier to nucleate at grain boundaries. As the Z value decreases gradually, the recrystallization mechanism transitions from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX). At a low Z values with the strain rate of 0.001 s-1, the inhibitory effect of rare earths weakens, resulting in a comparable recrystallization ratio between Al-Zn-Mg-Cu-Gd alloy and 7075 aluminum alloy. Moreover, the average grain size of the aluminum alloy with Gd addition is only half that of 7075 aluminum. The addition of Gd provides Orowan and substructure strengthening for the alloy, which greatly improves the work-hardening of the alloy compared with 7075 aluminum alloy and improves the strength of the alloy.