稀土铒、铈改性AZ91镁合金应力腐蚀行为研究*

摘要

AZ91 magnesium alloys modified by erbium(Er)and cerium(Ce)(AZErCe)were fabricated by casting into metal mold.The effect of Er and Ce on the microstructure and stress corrosion cracking(SCC)behavior of AZ9 1 in Cl-containing moist atmosphere was investigated by slow strain rate tensile(SSRT)tests,potentiodynamic polarization analysis,X-ray photoelectron spectroscope(XPS),scanning electron microscope(SEM)and X-ray diffraction(XRD).The results showed that the β-Mg17Al12 phase was transformed from discontinuous network into small island distribution and dispersed homogeneously after the addition of Er and Ce,and the formation of Al3Er and Al11Ce3 intermetallic compounds reduced the volume fraction ofβ-Mg17Al12 phase.The addition of Er and Ce greatly improved the SCC resistance,because the local corrosion resistance of AZErCe was improved by alleviating the cathodic effect ofβ-Mg17 Al12phase and improving the compactness of the surface films.As a result,the processes of initiation and expansion of cracks were suppressed and the influence of hydrogen embrittlement on SCC resistance was weakened.The fractography of SCC was changed from brittle cleavage fracture into quasi-cleavage frac-ture,and the local corrosion at the edge of fracture surfaces was greatly alleviated.%通过金属型浇铸方法制备稀土铒(Er)、铈(Ce)改性AZ91镁合金(AZErCe).采用慢应变速率拉伸(SSRT)试验、动电位极化测试、X射线光电子谱(XPS)、扫描电镜(SEM)以及X射线衍射(XRD)等方法研究Er、Ce对AZ91镁合金显微组织以及在含Cl-湿大气下应力腐蚀开裂(SCC)行为的影响.结果表明,稀土Er、Ce添加后,β-Mg17Al12相由不连续网状分布转变为细小的弥散岛状分布,并生成Al3Er和Al11Ce3金属间化合物,减少β-Mg17Al12相的体积分数;通过抑制β-Mg17Al12相的阴极作用,提高表面膜的致密性,改善合金抗局部腐蚀性能,阻滞裂纹的萌生、扩展以及弱化氢脆的影响,Er、Ce 极大提高了AZ91镁合金的抗应力腐蚀性能,合金的应力腐蚀断口由脆性解理断裂转变为准解理断裂,且断口边缘局部腐蚀程度大大减轻.