| The research work of this thesis was carried out based on research projects with national defense and military industry"military lightweight materials and components of the natural environment and corrosion control technology research"(D1020060943). 7B04 high-strength aluminum alloy and protective coating, which was extremely promising in aviation industry, was was taken as research object. Through developing comparison experimental study of outdoor atmospheric exposure and shed atmospheric exposure of offshore platforms, and comprehensive utilization of SEM, EDS, XRD, infrared spectroscopy, and other modern sophisticated analytical tools, the severity of exposure environment for protective coating aging damage and aging mechanism was revealed. 7B04 aluminum alloy corrosion behavior and dynamic rules was studied from the macro and micro scale to research. The electrochemical characteristics of different aging damage degree of protection coatings in 3.5% NaCl solution was studied by using the advantages of electrochemical technology, which was tried to establish correlation of electrochemical characteristic parameters of coating and the actual degree of corrosion damage. The main research results are as follows:(1) A typical characteristic of exfoliation corrosion of 7B04 aluminum alloy was appeared in marine atmospheric environment, and the corrosion evolution process was from the beginning of pitting corrosion, and gradually evolved to intergranular corrosion, and exfoliation corrosion. The exfoliation corrosion has great influence on the effective section size, strength and plasticity index of 7B04 aluminum alloy. After test for 3 years, the elongation percentage after fracture has dropped 80% and the tensile strength retention rate of part of the sample was less than 50%, which cannot meet the requirements.(2) The corrosion kinetics was established based on corrosion depth index of 7B04 aluminum alloy, which meet power function law. The fitting result of offshore platforms outdoor is y=10.927x2.190,the n values up to 2.19; the fitting result of offshore platforms shed is y=46.67x1.703, the n values up to 1.7, which showed that marine platform environment has high acceleration for the corrosion effect of 7B04.(3) The pitting potential of 7B04 aluminum alloy in 3.5% NaCl solution was about -0.735 V, which was lower than that of the most self-passivating characteristics metal and alloy. The pitting potential of 7B04 aluminum alloy was close to its corrosion potential, which was easily happened pitting corrosion in atmospheric environment. Meanwhile, SEM, TEM microscopic analysis showed that, in 7B04 plank in the process of rolling grains were severely stretched parallel to the rolling direction. after heat ageing peak T6, along the grain boundary precipitates smaller and semi-continuous distributionηphase, precipitation Free Zone (PFZ) is not obvious. The corrosion potential difference betweenηphase and 7B04 aluminum alloy matrix leads to preferential dissolution ofηphase as the anode and forms an anodic dissolution channel along the grain boundary, which is an important reason of intergranular corrosion.(4) For TS96-71 fluorinated polyurethane coatings exposed to marine atmosphere, UV light can cause chain scission of molecular chain carbamates, resulting in carbonyl index fell to 0.0556 from the original 0.3953. With the dramatic reduction of carbonyl index, resin macromolecules degraded, the bond package role of pigments significantly decreased, the coating surface began to precipitate a large number of small pigment particles, which leading to increased macro-and micro-defects.(5) The electrochemical behavior of multi-layer protective coating system in sea air outdoor exposure to different cycles was studied and the equivalent circuit model corresponding with different aging damage degree was established by using ac impedance spectroscopy technology, and the impedance spectroscopy was analyzed reasonably. The results showed that sulfuric acid anodizing + TB06-9 + TS96-71 protective coating system was pulverization serious, but only affects the finish layer, and the second resistance R2 maintains between 1081010Л·cm~2. The overall resistance is up to 109Л·cm~2, which shows that the coating system still has a good protective effect.
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