Creep behaviors and microstructure evolution of Mg-5Y-2Nd-3Sm-0.5Zr alloys

The creep behaviors and microstructure evolution of Mg-5Y-2Nd-3Sm-0.5Zr alloy under the temperature 473 K–523 K and the stress 70 MPa–110 MPa for 100 h were investigated in a typical creep testing machine. The results show that the creep strain of Mg-5Y-2Nd-3Sm-0.5Zr alloy increases with the increase of temperature and stress. The steady-state creep rates at 523 K/70 MPa and 523 K/90 MPa are only 2.3611 × 10−8s−1 and 3.9194 × 10−8 s−1, the creep strain after 100 h is only 0.735% and 1.751%, Mg-5Y-2Nd-3Sm-0.5Zr alloy has excellent creep resistance under 523 K. When the stretching temperature is the same, the grain size of the alloy increases with the increase of tensile strength. Under the same tensile strength, with the increase of temperature, the grain size of the alloy increases obviously with the increase of temperature. The creep stress exponents (n) are 0.84 at 473 K, 2.58 at 498 K and 5.13 at 523 K under the creep conditions of 70 MPa–110 MPa. In addition, the creep activation energy Q c increases with the increase of stress. The creep activation energies Q c are 96.85 kJ mol−1, 113.48 kJ mol−1 and 181.24 kJ mol−1 for 70 MPa, 90 MPa and 110 MPa, respectively. The results of stress exponents and creep activation energies show that the creep mechanism of aging Mg-5Y-2Nd-3Sm-0.5Zr alloy changes from grain boundary slip to dislocation slip with the increase of creep temperature and stress.