Effects of Interfacial Damage on Corrosion Protection

It is a well-established practice to test corrosion resistance of a coated panel by exposing a scribed coating layer to a corrosive environment such as salt spray for a prolonged period. Corrosion resistance of the coating is qualitatively evaluated by examining the corrosion that took place near the scribed line. Such a method certainly provides an estimate of the level of corrosion resistance of the coating however, this method does not yield information concerning the mechanisms of corrosion protection. 

Salt Spray Test With Different Scribes 

In contrast, the spinning tracks were clearly observed in the scribes made in spinning mode (designated as U shape). Spinning left burrs in the scribes and also wider scribes. Since they provided more exposed surface area, the left burrs in the scribe may have a greater chance to initiate the corrosion. 

After completing test cycles in Prohesion salt spray, the panels were rinsed with distilled water and visual observations were made. Then the panels are subjected to a commercial paint stripper solution (Turco 5469) to strip off the E-coat on the scribed surface to see the corrosion underneath the E-coat film and away from the scribe. 

Concurrent EIS Measurement with Prohesion Salt Spray 

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