A Cyclic Model of Cosmetic Corrosion for Painted Steel Sheets

To identify the most significant parameters influencing the cosmetic corrosion of cold-rolled and coated steel sheets, stretch deformed panels were phosphated, painted and exposed in real time on an experimental car for 5 years.

Based on advanced microanalysis techniques, the morphologies and the chemical composition of the corrosion salts are characterized. Comparisons between accelerated tests and natural exposures are made and corrosion mechanisms are identified.

On that basis, a 3-step cyclic model of cosmetic corrosion is presented. Combined with the experimental results, this model outlines the importance of the coating characteristics, the compositions of the corrosion products, the humidity and temperature cycles during the exposure tests (natural or accelerated) and the environmental conditions (salts and polluting gases) on the corrosion mechanisms and the resistance of painted coated steels.