Y对高锌镁合金的拉伸蠕变行为的影响

Tensile Creep Behavior of Y Addition in High Zinc Magnesium Alloy

采用扫描电镜,X 射线衍射仪以及高温蠕变试验机等试验手段研究了 Y 含量对 Mg-5.5Zn 重力铸造镁合金抗蠕变性能和应力指数的影响.结果表明：随着 Y 含量的增加,Mg-5.5Zn 合金中依次出现了 Mg7 Zn3,Mg3 Zn6 Y（I-相）和 Mg3 Zn3 Y2（W-相）3种不同类型的强化相,而合金中第二相种类、体积分数发生变化,导致抗蠕变性不断提高.在同样的蠕变条件下,高熔点稀土相比低熔点 Mg7 Zn3相更能降低合金的稳态蠕变速率.Mg-5.5Zn-（0.7,1.5,3.5）Y（wt%）3种合金在175℃/50~60 MPa 下的应力指数 n 分别为5.2,3.2和2.2,在200℃/50~60 MPa 下应力指数 n 分别为11.0,3.8和2.9.Mg-5.5Zn-0.7Y合金在175℃/55 MPa 和200℃/55 MPa 条件下的蠕变机制分别为位错攀移和 Power-Law 方程失效.Mg-5.5Zn-（1.5,3.5）Y 两种合金在175~200℃/50~60 MPa 范围下的蠕变机制是位错粘滞运动.

The effect of earth element Y addition on the creep properties and creep stress exponent of Mg-5.5Zn gravity cast magnesium alloy was investigated by using scanning electron microscopy（SEM）,X-ray diffraction（XRD）and creep property testing at elevated temperature.The results show that,with the increase of yttrium content in Mg-5.5Zn （wt%）alloy ,three second phases,Mg7 Zn3 ,Mg3 Zn6 Y（I-phase）and Mg3 Zn3 Y2 （W-phase）,are found.The variety categories and the increasing volume fraction of the second phase cause the increase of the creep resistance obviously.Compared with Mg7 Zn3 phase,rare earth phases have a high melting point and it have a stronger effect for reducing the creep rate of alloy in the same given creep conditions.When the applied stresses are 50 ~ 60 MPa at the temperature 448 K,the calculated stress exponent n is 5.2,3.2,and 2.2,respectively for the as-cast Mg-5.5Zn-Χ%Y（Χ=0.7,1.5,3.5）al-loys.The results indicate that the rate controlling mechanism of Mg-5.5Zn-0.7Y alloy at 175 ℃/55 MPa and 200 ℃/55 MPa is respectively the dislocation creep and power law breakdown,and the creep mecha-nism of Mg-5.5Zn-（1.5,3.5）Y two alloys is dislocation viscous motion at the applied stresses of 50 ~60 MPa and the temperature of 448~473 K.