钆改性镁合金在溶液中的应力腐蚀行为研究

Stress Corrosion Behavior of Gadolimium Modified Magnesium Alloys in Solution

通过添加质量分数为0.5%,1%,1.5%和2%的Gd对AM50镁合金进行改性,采用金相显微镜、X射线衍射、扫描电子显微镜及腐蚀慢应变速率拉伸研究了目标金属在空气、去离子水和NaCl溶液中的应力腐蚀行为。结果表明,Gd添加后,合金组织中出现了白亮的颗粒状金属间化合物Al_(2)Gd,随着Gd添加量的增加,Al_(2)Gd相的数量和体积增加,而β-Mg_(17)Al_(12)相的数量和体积减少。慢拉伸实验结果显示,在纯水中,随着合金中Gd的含量增加,合金的抗应力腐蚀能力增加;而在NaCl溶液中,0.5%Gd的添加量显示了最优的应力腐蚀抗力。此外,Gd的添加没有改变合金的断裂机制,依旧为准解理断裂。应力条件下,由于腐蚀导致的蚀坑形核和发展是试样最大断裂强度下降的直接原因。随着Gd的含量在合金中增加,膜破裂机制在试样断裂过程中导致的试样形貌变化是试样失效的主要原因。

AM50 magnesium alloy was modified by adding rare earth element Gd with mass fraction of 0.5%,1%,1.5%and 2%.The stress corrosion behavior of these samples in air,deionized water and NaCl solution was studied by an optical microscope,X-ray diffraction,a scanning electron microscope and corrosion slow strain rate tensile test.The results show that the white granular intermetallic compound Al_(2)Gd appears in the alloy structure after Gd addition.With the increase of Gd addition,the quantity and volume of Al_(2)Gd increase while theβ-Mg_(17)Al_(12)decrease.The slow tensile test results show that the anti-stress corrosion sensitivity increases with the addition of Gd in deionized water.In NaCl solution,the AM50+0.5%Gd Mg alloy shows the best stress corrosion resistance.In addition,Gd addition does not change the fracture mechanism of the alloy,which is still quasi cleavage fracture.Under stress conditions,the pitting and development caused by corrosion is the direct reason for the decrease of the ultimate tensile strength.With the addition of Gd,the change of specimen morphology caused by film fracture mechanism in the process of specimen fracture is the main reason for samples'failure.