| 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 IIexfoliation 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.
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