化成処理鋼板の白錆の定量的外観評価技術

抄録

In relation to the evaluation of corrosion resistance of zinc-coated steel sheets with chemical conversion coatings, evaluation of white rust occurrence is commonly conducted by visual observation of the specimens. However, because large individual variation exists in evaluation by visual observation and minute white rust is generated on the specimen surface, it is difficult to evaluate corrosion resistance objectively. An evaluation method was developed to appropriately evaluate the corrosion resistance of zinc-coated steel sheets with chemical conversion of coatings. It can visualize minute white rust accurately using low-angle lighting, a line scan camera, and a linear stage. Furthermore, the corrosion area ratio of the white rust can be evaluated quantitatively using image analysis. Good correlation was found between the developed quantitative analysis method and evaluation by visual observation.
The developed quantitative analysis method is applicable to various corrosion tests such as the exposure test, the salt spray test (SST), the combined cyclic corrosion test (CCT), and a new accelerated corrosion test (ACTE: Accelerated Corrosion Test for Electrical appliances). Superior correlation was found between the ACTE results and corrosion in actual environments. The ACTE test can estimate the influence of the amount of deposited sea salt on corrosion resistance of materials. The ACTE test and the developed quantitative analysis method enable appropriate evaluation of the corrosion resistance of zinc-coated steel sheets with chromate-free coatings.