The Relative Effect of Paint Film Thickness on Bimetallic and Crevice Corrosion

The proliferation of Unibody construction, for vehicle weight reduction, and the expanded use of precoated steel, for improvement in outer body rust-through protection, has significantly increased the number of bimetallic and crevice unions on U.S. manufactured vehicles. Cyclic corrosion and proving ground testing has shown that these unions are highly active electrochemically, resulting in extensive anodic corrosion and cathodic delamination of the paint film. This work examines the individual contribution of each layer of the applied protective coatings package, with respect to applied film thickness, to the reduction of permeation by water, oxygen, and NaC1 and resultant corrosion.