Evaluation of surface tortuosity on the corrosion resistance of organic coatings using laser texturing process

Surface tortuosity is a quantitative measure of the complexity of a material's surface. It is commonly defined as the ratio between the real length of the surface over the shortest distance between two points on the surface. An increase in surface tortuosity has been found to have advantageous effects on the durability of coated parts when exposed to corrosive and humid conditions. Laser surface texturing, a versatile process, can be used to modify the surface tortuosity by creating various structure patterns on the surface of steel. This study aims to investigate the impact of V-shaped groove dimensions on the resistance against corrosion creep of an organic coating applied to textured surfaces. Comparative surface tortuosity measurements were obtained for different groove dimensions while keeping the aspect ratio and textured areas constant. V-shaped grooves with an aspect ratio of 1 and sizes of 50, 100, and 200 μm were machined on carbon steel AISI-A36. The distance between adjacent grooves was varied to achieve different textured areas, ranging from 10% to 60%. The surface roughness (Sa) and surface tortuosity were characterized. The performance of the coating was evaluated using an accelerated corrosion test based on ISO 12944-9. The results indicate that V-shaped grooves with dimensions of 100 μm and a textured area of 40% exhibit the lowest coating delamination. It is worth to mention that the performance of organic coatings is enhanced up to a certain optimal point by an increase in surface tortuosity. However, beyond this optimal point, further increases in tortuosity do not lead to an increased resistance to the propagation of corrosion.