【作者】 尹淑英；

【导师】 陈立佳； 马春艳；

【作者基本信息】 沈阳工业大学 ， 材料学， 2012， 硕士

【摘要】 由于具有密度低、比强度高、阻尼性能良好等优良性能,近年来,镁合金尤其是采用热挤压技术制备的变形镁合金已经得到越来越多的关注。为了研究稀土元素Y以及不同热处理对热挤压Mg-7%Zn-0.6%Zr系镁合金的疲劳行为的影响,对挤压态、时效态和固溶+时效态的Mg-7%Zn-0.6%Zr(-0.5%Y)合金进行了室温低周疲劳实验。实验结果表明,不同处理状态的热挤压Mg-7%Zn-0.6%Zr(-0.5%Y)合金表现为循环应变硬化和循环稳定。稀土元素Y的添加可以提高挤压态Mg-7%Zn-0.6%Zr合金在较高外加总应变幅下的循环变形抗力,可以提高时效态合金在绝大多数外加总应变幅下的循环变形抗力,可以提高固溶+时效态合金在各个外加总应变幅下的循环变形抗力。时效处理可以提高热挤压Mg-7%Zn-0.6%Zr(-0.5%Y)合金在每个外加总应变幅下的循环变形抗力。固溶+时效处理对热挤压Mg-7%Zn-0.6%Zr合金的循环变形抗力的影响较为复杂,但可以提高热挤压Mg-7%Zn-0.6%Zr-0.5%Y合金在绝大多数外加总应变幅下的循环变形抗力。稀土元素Y的添加可以明显提高挤压态和固溶+时效态Mg-7%Zn-0.6%Zr合金的低周疲劳寿命,同时可以提高时效态Mg-7%Zn-0.6%Zr合金在较低外加总应变幅下的低周疲劳寿命。时效处理可以改善热挤压Mg-7%Zn-0.6%Zr合金在较高外加总应变幅下的低周疲劳寿命,但会降低热挤压Mg-7%Zn-0.6%Zr -0.5%Y合金的低周疲劳寿命。固溶+时效处理可以提高热挤压Mg-7%Zn-0.6%Zr (-0.5%Y)合金在较高外加应变幅下的低周疲劳寿命。对于不同处理状态的热挤压Mg-7%Zn-0.6%Zr(-0.5%Y)合金而言,其载荷反向周次与弹性应变幅之间服从Basquin公式,同时与塑性应变幅之间服从Coffin-Manson公式。在外加总应变控制的低周疲劳加载条件下,不同加工处理状态的热挤压Mg-7%Zn-0.6%Zr(-0.5%Y)合金的疲劳裂纹均以穿晶方式于疲劳试样表面萌生,且以穿晶方式进行扩展。更多还原

【Abstract】 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.更多还原