The effect of surface profile on coating adhesion and corrosion resistance

Coatings on machined surfaces are generally found to degrade early and this has been attributed to poor adhesion. Good adhesion normally requires blasting, but surfaces machined for functional requirements, such as seal (flange surface) or assembly (tightness of nuts) are not blasted before being coated. The effect of surface roughness, peak density and contact area on coating adhesion and protective performance has been studied. Machined and grit blasted samples have been tested for corrosion creep, cathodic disbonding and adhesion. The results showed that machined surfaces have lower contact area than blasted samples. The contact area increased with decreasing peak density for both blasted and machined samples. Adhesion loss was however positively related to the contact area on machined surfaces and inversely related on blasted surfaces. High peak density seems to be key factor for increasing coating adhesion on machined surfaces, while a high peak density seemed to decrease adhesion on profiles with sharp features and high surface roughness.