What is ISO 9227?
In a salt spray test according to ISO 9227, corrosion occurs relatively quickly in any galvanized or diffusion galvanized coating. This while in nature, depending on the layer thickness, it is resistant to rust formation for longer than tested. The explanation? In these accelerated tests, the zinc layer cannot build up a protective patina layer, which explains the rapid failure.
According to EN ISO 14713, accelerated corrosion tests on zinc coatings say little about the results in practice.
What guarantee does ISO 9227 offer?
With the application of a passivation or a topcoat, an additional passive protection is applied, so that even thin zinc layers achieve excellent results in a salt spray test. The quick test then proves the closedness, the passivity and the connectedness of the entire system. In practice, the topcoat protects the active protective layer until it is damaged by cracks, scratches or mechanical influences. At that moment, the basecoat itself actively fills the impurities that have arisen and the protection remains intact. Duplex systems are therefore significantly stronger than single zinc coatings.
