Hot deformation behavior and microstructure evolution of Mg-Gd-Y(-Sm)-Zr alloys

Abstract

We investigated the deformation behavior of Mg-Gd-Y(-Sm)-Zr alloys during high-temperature uniaxial compression (T = 350 °C, 400 °C, 450 °C and 500 °C; ε̇=0.003 s−1, 0.01 s−1, 0.1 s−1 and 1 s−1). The dynamic recrystallization (DRX) critical strain of Mg-Gd-Y(-Sm)-Zr was calculated, and its accuracy was verified by the transmission electron microscope (TEM). The hot deformation activation energy and constitutive equation after hot compression were calculated. The effect mechanism of Sm on microstructure evolution was also analyzed by the electron backscatter diffraction (EBSD) and TEM. It can be concluded that the hot deformation activation energies of Mg-Gd-Y-Zr and Mg-Gd-Y-Sm-Zr were 206.17 kJ/mol and 263.07 kJ/mol, respectively. The addition of Sm can increase flow stress and make DRX occur earlier. With the increase of strain, Sm delayed the DRX by inhibiting the activity of pyramidal<c+a> slip. Under the deformation condition of 400 °C/0.003 s−1/0.7, the continuous dynamic recrystallization (CDRX) mechanism was dominant in Mg-Gd-Y-Zr and Mg-Gd-Y-Sm-Zr. In addition, the dynamic precipitation phase after adding Sm was the β-Mg5(Gd, Y, Sm) equilibrium phase with a face-centered cubic structure. There was a staggered chain distribution between DRX grains and precipitates at the original deformation grain boundary, which effectively hinders dislocation rearrangement and grain boundary migration. Finally, we constructed the DRX mechanism diagram and the interaction diagram between the precipitated phase and DRX grains.’