Effect of precipitates on creep behavior of the extruded Mg-9Gd-8Y-2Nd-1.2Zr-T5 at 250 °C

Creep tests of the extruded Mg-9Gd-8Y-2Nd-1.2Zr-T5 were carried out under different stresses at 250 °C. The relationship between microstructures and creep resistance of the alloy was studied. The result shows that the extruded Mg-9Gd-8Y-2Nd-1.2Zr-T5 has the excellent creep resistance at 250 °C. The steady-state creep rate increases from 3.92E−09 to 2.27E−08 with increasing stress from 40 MPa to 100 MPa and is insensitive to the stress. The grain boundary sliding is considered as the main creep mechanism of the extruded Mg-9Gd-8Y-2Nd-1.2Zr-T5 at 250 °C. The large amounts of β′ phase with good heat stability precipitates in the grain of the extruded Mg-9Gd-8Y-2Nd-1.2Zr-T5, inhibits the dislocation sliding and grain boundary sliding, and increases creep resistance. The transformation of β′ phase to β phase and the appearance of the precipitate-free zone during creep process are related to grain boundary sliding accompany with precipitates dragged and dissolution. The reduction in the numbers of β′ phase, the appearance of the precipitate-free zone and the β phase with thick lath shape precipitating at grain boundary reduce creep resistance and deteriorate the creep property.