Creep properties and creep microstructure evolution of Mg-2.49Nd-1.82Gd-0.19Zn-0.4Zr alloy

The creep properties and creep microstructure evolution of Mg-2.49Nd-1.82Gd-0.19Zn-0.4Zr alloy were investigated as a function of creep stresses and creep temperatures. It was found that the creep strain and the creep rate increases but the creep life decreases with increasing creep temperatures and creep stresses. At a defined creep stress, the creep strain increases with increasing creep temperatures. At a defined creep temperature, the creep strain increases with increasing creep stresses. α(Mg), Mg₁₂Nd phase and Mg₅Gd phase are present in the microstructure after creep. Furthermore, the Mg₁₂Nd phase appears to increase with increasing the creep stress, creep temperature and creep time, indicating that the creep stress, creep temperature and creep time may have a significant effect on the formation of the equilibrium Mg₁₂Nd phase during the creep. At the temperature range less than 225 ℃, the calculated Q_c value is about 74–98 kJ/mol, which is very close to the grain boundary diffusion activation energy (80 kJ/mol⁻¹), indicating that the grain boundary sliding may be a dominant factor affecting creep properties. While, at the temperature range higher than 225 ℃, the calculated Q_c value is about 227–289 kJ/mol, which is much higher than the self - diffusion activation energy (135 kJ/mol⁻¹), indicating that the dislocation climbing may be a dominant factor affecting creep properties. The fracture was observed to occur along the grain boundaries. The initiation of the crack is from a trigeminal grain boundary, indicating that the Mg₁₂Nd phase at the grain boundary has a significant effect on the initiation of the crack.