For equipment serving in harsh tropical marine seawater/atmospheric corrosive environments, studying the variation law of stealth performance of radar absorbing coatings in corrosive environment, and revealing the mechanism of coating corrosion failure on radar stealth performance are of great benefit to extend the service life of absorbing coatings, ensure stable and reliable absorbing performance, formulate scientific and reasonable maintenance plans, and reduce maintenance costs. The work aims to study the variation law of absorbing coatings after corrosion failure and the stealth performance of radar. Firstly, 7 Q235 steel plates with a size of 120 mm×50 mm×2 mm were prepared. After sandblasting, a strontium chrome yellow primer layer with a thickness of (30±2) μm was sprayed. After cured at 80 ℃ for half an hour, the radar absorbing coating with a thickness of (0.58±0.05) mm was sprayed. After cured at 80 ℃ for 2 h, the 7 parallel samples were completed. Then, neutral salt spray test was carried out for 0 h (original samples not subject to salt spray test), 24 h, 48 h, 96 h, 240 h, 480 h and 840 h, and the composition and microstructure of the samples after the test were characterized with X-ray energy dispersive spectrometer and scanning electron microscope. Gmary Reference 3000 electrochemical workstation was used to perform electrochemical AC impedance spectroscopy test on the samples after salt spray test, and the equivalent circuit diagram was introduced to describe and fit the AC impedance data to further analyze the failure mechanism of the coating. The Agilent E8363C vector network analyzer was used to connect the terminal open circuit test fixture, and the 8-18 GHz radar wave reflectivity test was carried out on the samples after the test. After 96 h and 240 h salt spray test, there was visible local small-scale pitting corrosion on the absorbing coating, and after 480 h and 840 h, the corrosion phenomenon was obviously serious and large-area pitting corrosion occurred. At the same time, the morphology of the absorbent also changed, and the oxygen content of the coating increased, indicating that the absorbent in the coating was corroded and oxidized by the corrosive medium infiltrated. By fitting the results of the AC impedance spectrum data with the equivalent circuit diagram, it was found that the corrosion failure of the samples went through three stages. The first was the stage of rapid decline in the corrosion protection performance of the coating from 0 to 48 h. The corrosion medium penetrated from the coating surface to the entire coating. The second was the fluctuation stage of the protective performance of the coating from 48 to 480 h. The oxidation product was a substance with high resistance and low capacitance, which restored the resistance value of the coating to a certain extent. The third was the stage of further rapid decline of the protective performance of the coating from 480 to 840 h. At this stage, the deeper layer of the absorbent was corroded and oxidized. The final test result indicated that the film value dropped by 69.72% compared with that before the test, indicating that the protective performance of the coating was significantly damaged. However, the average reflectivity of the radar wave of the 0 h sample was –4.27 and the 4 dB bandwidth was 70.07%, while the average reflectivity of the 840 h sample was –4.71, and the 4 dB bandwidth was 87.53%. The average difference of the reflectivity test results during the whole test process was less than 0.5 dB, indicating that the radar stealth performance did not decline. In the 0-840 h salt spray test, the absorbents were corroded and oxidized, but the stealth performance of radar absorbing coatings did not still decrease. In a certain period of time, the absorbents in radar absorbing coating are oxidized and corroded, which does not lead to the decline of radar stealth performance. The general understandings of scholars have been broken through by the test result. The effect law and the action mechanism of coating corrosion failure on the radar stealth performance have been intensively studied. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.
