【作者】 张正；

【导师】 宋诗哲；

【作者基本信息】 天津大学 ， 应用化学， 2004， 硕士

【摘要】 飞机结构材料LY12CZ铝合金在含Cl-的潮湿大气环境中易发生点蚀，进而发展到晶间腐蚀和剥蚀。本文运用电偶方法研究了含Cl-和NO3的薄液膜下LY12CZ腐蚀行为，进一步研究了NaCl溶-液中不同剥蚀程度LY12CZ的EIS特征，并结合表面腐蚀形貌对铝合金剥蚀状态进行了分类和判断。主要实验工作及结果如下：设计制作了安装有自制Ag/AgCl固体参比电极的纯Cu-LY12CZ电偶电池。建立了简单的实验室模拟潮湿大气环境。研究结果表明：阴阳极面积比大的电偶电池Ig值受薄液膜中Cl-浓度影响较大。阴阳极面积比小的电偶电池阳极金属腐蚀主要受阴极氧扩散控制。薄液膜中NO3浓度升高将抑制Cl-的作用，使LY12CZ-处于全面腐蚀状态，Ig值随NO3浓度升高呈线性下降。本体溶液-中电偶电池Ig值主要受阴极氧扩散控制，且小于相同Cl-浓度薄液膜下的Ig值。由Ig值计算阳极金属Icorr值具有一定可行性。EXCO溶液浸泡腐蚀制备不同剥蚀程度的LY12CZ试样，观察表面腐蚀形貌并对其剥蚀状态分类。研究0.1mol/LNaCl溶液中不同剥蚀程度LY12CZ的EIS特征，根据这些特征可对铝合金剥蚀状态进行分类和判断。0.6mol/LNaCl溶液中不同剥蚀程度铝合金EIS特征与0.1mol/LNaCl溶液中基本相同。铝合金的剥蚀状态可分为4个基本类型：未腐蚀及腐蚀轻微、点蚀萌生、剥蚀形成和剥蚀发展。选取江津大气腐蚀实验站试样大气暴露铝合金支架进行EIS测试，并根据EIS特征定性判断其处于剥蚀发展状态，结合试样表面腐蚀形貌验证了判断的合理性。铝合金表面氧化膜的不同状态，腐蚀产物在剥蚀的形成发展过程中的作用，以及表面腐蚀形貌特征，均对应着不同的EIS特征。Bode图相角峰的变化最具代表性。高频相角峰反映了铝合金表面氧化膜的状态；腐蚀反应形成了低频相角峰。腐蚀产物的机械阻挡作用主要表现为Nyquist图低频率段的Warburg阻抗。更多还原

【Abstract】 LY12CZ aluminum alloy is a kind of aviation structure materials.When it is used in the moist atmosphere containing Cl— pitting willeasily happen and intergranular corrosion as well as exfoliationcorrosion will then be induced. In this paper the galvanic-couplemethod has been used to study the corrosion behavior of LY12CZaluminum alloy covered with thin electrolyte membrane in whichCl— and NO3 — are present. EIS characteristics of LY12CZ alloysamples in different exfoliation corrosion grades are studied in NaClsolution. And the exfoliation corrosion states of aluminum alloys areclassified and evaluated according to their corrosion morphologiesand EIS characteristics.The main experiments and results are showedas follow: The galvanic-couple electrochemistry cell is designed andconstructed which is composed of LY12CZ aluminum alloy as anodeand cuprum as cathode. A simple suit of experiment system, which iscapable of simulating moist atmosphere environment, is established.The results show that the concentration of Cl— strongly influences Igof galvanic-couple cell, in which the area ratio of cathode andanode is big. However the corrosion of anodic metal is mainlycontrolled by the diffusion of oxygen, when the area ratio of cathodeand anode is small.When the concentration of NO3 increases, the —action of Cl— will be restrained under the thin layer electrolyte,which makes LY12CZ in the uniformity corrosion state. The value ofIg shows linear decrease when the concentration of NO3 — increases.In the NaCl bulk solution the value of Ig of the galvanic-couple cellis mainly affected by the diffusion of cathodic oxygen and it is lessthan the value in the thin layer electrolyte with the sameconcentration of Cl— . It is doable to calculate the value of Icorr ofthe anodic metal according to Ig . Immersed in EXCO solution LY12CZ alloy samples in different II<WP=4>exfoliation corrosion grades are prepared. The corrosionmorphologies of samples are observed and the exfoliation corrosionstates of aluminum alloys are classified. The characteristics ofelectrochemistry impedance spectroscopy (EIS) of LY12CZ alloysamples in different exfoliation corrosion grades are studied in the0.1mol/L NaCl solution, according to which the exfoliation corrosionstates of aluminum alloys are classified and evaluated.Thecharacteristics of electrochemistry impedance spectroscopy ofaluminum alloys in different exfoliation corrosion grades in the0.6mol/L NaCl solution resemble to that in the 0.1mol/L NaClsolution. The exfoliation corrosion of aluminum alloys can beclassified into four states as follow: not corrode and faintly corrode,pitting corrosions happen, exfoliation corrosions come forth andexfoliations develop. The aluminum alloy bracket exposed in theatmosphere of JIANG JIN experimental station is chosen to be testedby EIS, on which samples are placed. And it is qualitatively decidedto reside developing state of aluminum alloys exfoliation by thecharacteristics of electrochemistry impedance spectroscopy. Thejudgment proves to be reasonable by the corrosion morphologies ofthe samples. Different states of oxidative film on the surface of aluminumalloys, the actions of the corrosive products in the growing processof exfoliation corrosion, and the corrosion morphologies allcorrespond to different characteristics of electrochemistry impedancespectroscopy. The change of phase in the Bode graph is typical. In thesection of high frequency, the peak of phase reflects different statesof oxidative film on the surface of aluminum alloys. In the section oflow frequency the peak of phase is formed by corrosive reaction. TheWarburg impedance in the low frequency section of the Nyquist graphshows the mechanical counterchecks of the corrosive products.更多还原