Improving the Galvanic Properties of Zinc-Rich Organic Coatings by Corona Discharge Treatment 850209
Zinc-rich organic precoated steel sheet is an attractive product for corrosion-resistant automotive applications due to its formability, weldability, availability and cost. A disadvantage of this product is an inability of the coating to provide a significant level of cathodic protection to areas of the steel base exposed to the environment at sites of damage to the coating. To gain increased understanding of this behavior, we studied the galvanic properties of zinc-rich organic coatings with electrochemical, microscopic and electronic methods. We observed high electrical resistances within these coatings that preclude effective galvanic protection of steel by the zinc in the coating. Based on these studies, we discovered that corona-discharge treatment, an inexpensive electric discharge treatment, significantly increases the coating's conductivity and galvanic activity. Compared to untreated coatings, corona-discharge treated coatings show significantly higher levels of galvanic protection in electrochemical and accelerated corrosion tests.