AZ31B镁合金表面镨盐转化膜的制备及性能研究

Preparation and properties of praseodymium salt conversion film on AZ31B magnesium alloy

稀土盐化学转化法是一种改善AZ31B镁合金耐蚀性能的有效方法。本文选用化学转化技术,将硝酸镨作为转化液的主要物质,在AZ31B镁合金表面生成不同程度的微米级镨盐转化膜层,利用电化学测试技术、析氢实验和点滴实验评价不同膜层的耐蚀性。结合扫描电镜、X射线衍射仪、能谱仪和X射线光电子能谱探究镨盐转化膜的表观形貌和组成结构。结果表明:镁合金表面生成一层致密膜层,膜层的主要组成元素为Pr和O,主要构成物质是氢氧化镨和镨的部分氧化物。当Pr(NO3)3·6H2O质量浓度为18 g·L-1时,制备的膜层表面裂纹缺陷较少,较为光滑致密,试样的耐蚀性能最佳,自腐蚀电流密度相比镁合金试样下降了4个数量级,自腐蚀电位相比镁合金试样正移了大约800 mV,电化学交流阻抗谱同样显示该试样的电荷转移电阻和膜层电阻最大,相对于其他试样有了显著提升。

Rare earth salt chemical conversion method is an effective method to improve the corrosion resistance of AZ31B magnesium alloy.In this experiment,the chemical conversion technology was se‐lected.Praseodymium nitrate was used as the main substance of the conversion solution to form differ‐ent degrees of micron-scale praseodymium salt conversion film on the surface of AZ31B magnesium al‐loy.The apparent morphology and structure of praseodymium salt conversion film were studied by scan‐ning electron microscope,X-ray diffraction,energy dispersive spectrometer and X-ray photoelectron spectroscopy.The results show that a dense film is formed on the surface of magnesium alloy.The main components of the film are Pr and O,and the main components are praseodymium hydroxide and some oxides of praseodymium.When the mass concentration of Pr(NO3)3·6H2O is 18 g·L-1,the prepared film surface has fewer crack defects,is relatively smooth and dense,and the corrosion resistance of the sam‐ple is the best.The self-corrosion current density is 4 orders of magnitude lower than that of magnesium alloy sample,and the self-corrosion potential moves forward by about 800 mV as compared with the magnesium alloy sample.The electrochemical AC impedance spectra also show that the charge transfer resistance and film resistance of this sample are the largest,which is significantly improved compared with other samples.