Creep mechanism of Mg-5.5Zn-2Gd-0.6Zr cast alloy

Mg-5.5Zn-2Gd-0.6Zr cast alloy was designed on the base of Mg-5Zn-0.6Zr (ZM-1) alloy by adding Zn and Zr. The experimental alloy samples were prepared by sand casting. The creep curves of the experimental alloy were tested under different temperatures and stresses. The results show that the creep resistance of Mg-5.5Zn-2Gd-0.6Zr alloy is much higher than that of the ZM-1 alloy. The creep activation energy (Q _200-250°C) of Mg-5.5Zn-2Gd-0.6Zr alloy under the stress of 40 MPa is equal to 142.0 kJ/mol, closing to the self-diffusion activation energy of magnesium, which shows that the dislocation climb plays a dominant role in the creep process of the experimental alloy at stress of 40 MPa. However, the activation energy (Q _200-250°C) of ZM-1 alloy at stress of 40 MPa is only 88.5 kJ/mol, closing to the grain boundary diffusion activation energy of magnesium, which means that the creep mechanism is grain boundary slip. The stress exponent (n) of experimental alloy at 200°C is equal to 4.21, while the stress exponent of ZM-1 alloy is 2.21. This also indicates that the creep mechanism of Mg-5.5Zn-2Gd-0.6Zr alloy at 200°C is dislocation climb.