Low-cycle Fatigue Behavior Of Hot-Extruded Mg-Zn-Zr-Y Alloy

Due to such excellent properties as low density, high specific strength and good damping capability, magnesium alloys especially wrought magnesium alloys prepared with hot extrusion technology have received more and more attention in recent years. In order to study the influence of rare earth element Y and different heat treatments on the fatigue behavior of hot-extruded Mg-7%Zn-0.6%Zr series magnesium alloys, the low-cycle fatigue tests for the Mg-7%Zn-0.6%Zr(-0.5%Y) alloys with as-extruded, aging as well as solid-solution plus aging states were performed at room temperature.The experimental results indicate that the cyclic stress response behavior of the hot-extruded Mg-7%Zn-0.6%Zr(-0.5%Y) alloys with different processing states exhibits both cyclic strain hardening and cyclic stability. The addition of rare earth element Y can enhance the cyclic deformation resistance of as-extruded Mg-7%Zn-0.6%Zr alloy at higher imposed total strain amplitudes, increase the cyclic deformation resistance of the alloy with aging states at most applied total strain amplitudes, and improve the cyclic deformation resistance of the alloy with solid-solution plus aging states at various imposed total strain amplitudes. The aging treatment can improve the cyclic deformation resistance of the hot-extruded Mg-7%Zn-0.6%Zr(-0.5%Y) alloys at each imposed total strain amplitude. The solid-solution plus aging treatment has complicated influence on the cyclic deformation resistance of the hot-extruded Mg-7%Zn-0.6%Zr alloy, but can enhance the cyclic deformation resistance of the hot-extruded Mg-7%Zn-0.6%Zr-0.5%Y alloy at most imposed total strain amplitudes. In addition, the addition of rare earth element Y can prolong the low-cycle fatigue lives of the hot-extruded Mg-7%Zn-0.6%Zr alloy with both as-extruded and solid-solution plus aging states, and can also enhance the low-cycle fatigue lives of the alloy with aging state at lower imposed total strain amplitudes. The aging treatment can improve the low-cycle fatigue lives of the hot-extruded Mg-7%Zn -0.6%Zr alloy at higher total strain amplitudes, but will reduce the low-cycle fatigue lives of the hot-extruded Mg-7%Zn-0.6%Zr-0.5%Y alloy. The solid-solution plus aging treatment can enhance the fatigue lives of the hot-extruded Mg-7%Zn-0.6%Zr(-0.5%Y) alloys at higher applied total strain amplitudes. For the hot-extruded Mg-7%Zn-0.6%Zr(-0.5%Y) alloys with different processing states, the relationship between the elastic strain amplitude and reversal cycles to failure is linear, and can be well described by the Basquin equation. Meanwhile, the relationship between the plastic strain amplitude and reversal cycles to failure also exhibits a linear behavior, and obeys the Coffin-Manson equation. Under the low-cycle fatigue loading condition with total strain control mode, the fatigue cracks initiate in a transgranular mode at the free surface of fatigue specimens, and propagate transgranularly for the hot-extruded Mg-7%Zn-0.6%Zr(-0.5%Y) alloys.