Research On Corrosion Detection Technologies For Typical Metals And Coating System In Nature Environment

Corrosion rates of metals exposed in environmental tests are often determined from the weight changes of specimens after corrosion product stripping. However, visual inspection or weight change measurements are not appropriate techniques to evaluate non-uniform corrosion and the early stage corrosion. In this paper, the digital image processing and electrochemical testing methods were used in aluminium alloy atmospheric corrosion and coating materials'corrosion detection research. The main conclusions are as follow:The corrosion morphology image acquisition systems were established which can be used both in the laboratory and filed. The suitable parameter to capture images and corresponding pre-processing methods were discussed and determined. In Beijing atmospheric corrosion exposure station, the image acquisition system was used to capture the early stage corrosion morphology of aluminium alloy specimens. After the denoise treatment, wavelet transformation was applied to decompose the improved images and energies of sub-images were extracted as character information. Based on the variation of image energy values, the corrosion degree of aluminium alloy specimens was qualitatively and quantitatively analyzed. The conclusion was basically identical with the result based on the corrosion weight loss.Periodic rain tests have been carried out for simulating atmospheric corrosion of aeronautical LC4CS and LY12CZ aluminium alloys. The digital image preprocessing and analysis method based on wavelet transformation was used to study the corrosion morphology of aluminium alloys samples. The canonical correlation analysis was used to gain the correlative coefficient between the energy values and the corrosion loss, through which an image feature parameterδwas extracted and discussed. The influences of orthogonal experiment parameters on acceleration were analyzed according to image feature parameterδwith analysis of variance (ANOVA) method, and the optimal parameters for accelerated corrosion test were also obtained. The result was shown to be consistent with that from weight loss method.An inspective method of corrosion surface damage of coating materials by using the digital image processing technology and correlative theories of colorimetry was discussed. The corrosion morphology image acquisition system was established, and it was used to capture the corrosion morphology of coating specimens, which were exposed in the field exposure station. To describe the discoloration of corrosion surface damages, we use the HSV color model. The Euclidean Distance between uncorroded image and corrode image was extracted as color characteristics parameter CP. This analysis develops a method for automated identification system of discoloration of corrosion damages, and is supposed to be an important step in the promising direction in corrosion inspection.The atmospheric corrosion field detective system of aluminium alloy based on electrochemical noise (EN) technology was presented. The environment sensitivity of different EN data acquisition systems was discussed. The electrochemical potential and current noise were acquired by aluminum alloy atmospheric corrosion sensor in natural atmosphere as well as the noise resistance. 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 electrochemical impedance spectroscopy (EIS) technology, electrochemical noise (EN) technology and digital image processing method were used to evaluate the degradation of the Q235 steel samples with different prime coating which have been exposed to the splash zone of Qingdao sea area with different times. The specimens'suface corrosion was quantitatively analyzed by image analysis. And with a high correlative coeddicent, 0.93, the linear relational model between the gray distribution of epoxy rich zinc primer coating specimens and electrochemical parameter-low frequency domain |Z0.01Hz| has been studied.