Mg-5.5Zn-2Gd-0.6Zr铸造镁合金的蠕变机制

在ZM-1(Mg-5Zn-0.6Zr)合金的基础上,适量增加Zn的含量并加入重稀土元素Gd,设计了Mg-5.5Zn-2Gd-0.6Zr实验合金。采用砂型铸造工艺制备实验合金试样,在不同温度和应力条件下对该实验合金和ZM-1合金的蠕变曲线进行了测试。结果表明:在相同条件下,Mg-5.5Zn-2Gd-0.6Zr实验合金的稳态蠕变速率较ZM-1合金的降低了一个数量级;当施加应力为40 MPa时,实验合金的蠕变激活能Q200-250℃=142.0 kJ/mol,接近镁的自扩散激活能,蠕变受位错攀移控制,而ZM-1合金在相同应力下蠕变激活能Q200-250℃=88.5 kJ/mol,接近镁的晶界扩散激活能,蠕变受晶界滑移控制。合金在200℃条件下的应力指数n=4.21,而ZM-1合金的应力指数n=2.21。因此,认为加入重稀土元素Gd后实验合金的蠕变机制发生改变,200℃时的蠕变机制为位错攀移机制。

Creep mechanism of Mg-5.5Zn-2Gd-0.6Zr cast alloy

Mg-5.5Zn-2Gd-0.6Zr cast alloy was designed on the base of Mg-5Zn-0.6Zr(ZM-1) alloy by adding Zn and Zr.The experimental alloy samples were prepared by sand casting.The creep curves of the experimental alloy were tested under different temperatures and stresses.The results show that the creep resistance of Mg-5.5Zn-2Gd-0.6Zr alloy is much higher than that of the ZM-1 alloy.The creep activation energy(Q200-250 ℃) of Mg-5.5Zn-2Gd-0.6Zr alloy under the stress of 40 MPa is equal to 142.0 kJ/mol,closing to the self-diffusion activation energy of magnesium,which shows that the dislocation climb plays a dominant role in the creep process of the experimental alloy at stress of 40 MPa.However,the activation energy(Q200-250 ℃) of ZM-1 alloy at stress of 40 MPa is only 88.5 kJ/mol,closing to the grain boundary diffusion activation energy of magnesium,which means that the creep mechanism is grain boundary slip.The stress exponent(n) of experimental alloy at 200 ℃ is equal to 4.21,while the stress exponent of ZM-1 alloy is 2.21.This also indicates that the creep mechanism of Mg-5.5Zn-2Gd-0.6Zr alloy at 200℃ is dislocation climb.