Research On Electrochemical Detection For Atmospheric Corrosion Of Aircraft Aluminium Alloy

Aircraft has played an important role in national economical construction and national defend security. The corrosion of high-strength aluminium alloys which are especially used as structural materials of aircraft will influence the aircraft's active time and security directly. It is significant to study the corrosion behaviour, field detective technique and corrosion resistance evaluation of high-strength aluminium alloy. Electrochemical corrosion occurred under the thin liquid film is the essential of high-strength aluminium alloy atmospheric corrosion. In this paper, high-strength aluminium alloy atmospheric corrosion electrochemical technologies were studied.The stability and continuity of thin liquid film formed on the surface of metal in the atmospheric environment are not so friendly to be tested by some traditional electrochemical methods. Electrochemical Noise (EN) is an in-situ and nondestructive technology, which is especially suited for studying local corrosion of metal materials. EN technology also can be used in the field detective of metal atmospheric corrosion due to its simple test equipments and low stability requirement of testing system. In this paper, an aluminium alloy atmospheric corrosion field detective method based on EN technology was presented. The electrode system was designed and fractured. The testing mode, data analysis and the system used in the field were discussed. The result of simulation experiments showed that the filed detective system established was suited for detection of aluminium alloy atmospheric corrosion; the data collected were able to reflect the influence that transformation of surface thin liquid film on aluminium alloy corrosion.The field detective system was used to study the corrosion behaviors of aluminium alloy (LY12CZ and LC4CS) in simulated paralic marine atmosphere and contaminative industrial atmosphere. The influence of Cl-,NO3- and SO42- ions in contaminative humid atmospheric environment on the corrosion behaviour of aluminium alloy were discussed. The results showed that NO3-and Cl- ions were the main factors to affect the corrosion type of aluminium alloy, the influences of the three anions in corrosion process of the aluminium alloys (LY12CZ and LC4CS) were complicated synergism, not simply superposed. Stress Corrosion Crack (SCC) is the most dangerous local corrosion type to high-strength aluminium alloy structure. EN technology was used to study the SCC generation and development of LY12CZ C-ring sample. EN potential spectrum characteristics were preliminary mastered. A quick corrosion sensitivity evaluation method was introduced.Aluminium alloys with surface treatment layer usually have good corrosion resistance in the active time, but corrosion still will occur in a proper condition and even more dangerous. Electrochemical Impedance Spectrum (EIS) technology was used to study the corrosion process of aluminium alloy with surface treatment layer. Some information about corrosion reaction occurred under the layer and the state of surface treatment layer were obtained from EIS. The result showed that the penetration of water and Cl- was the main factor to induce the pitting corrosion occurred under the surface treatment layer.