Influence of UV weathering on corrosion resistance of prepainted steel

It has been observed that UV weathering and corrosion resistance tests are often performed separately, without taking into consideration their reciprocal influence. This is the case in the field of prepainted steel, where the European norm considers either UV durability or corrosion resistance. There is therefore no real evaluation of the global durability of the system. The aim of the present study is to show the influence of the photo-oxidation of painted layers on their barrier effect. This can lead to the formation of small blisters during field exposure. The blistering observed in natural exposure is never observed in individual accelerated corrosion tests. The depth of degradation from the surface of prepainted panels has been determined with infrared spectroscopy. Successive abrasions and FTIR analysis in ATR mode (attenuated total reflectance) allow us to determine oxidation profiles that can be well correlated with the decrease of barrier properties of painted systems measured with electrochemical impedance spectroscopy (EIS). The blistering has then been reproduced by exposing UV-weathered samples in a salt spray device.