Accelerated corrosion tests of precoated sheet steels for automobiles

Precoated steel sheet is utilized extensively by the automobile industry in the production of vehicles with increased protection against corrosion. Laboratory accelerated corrosion tests such as the salt-spray test and the cyclic tests, which involve alternating cycles of saltwater immersion and humidity-chamber exposure, are widely used to make preliminary evaluations of the various precoated products. The results of salt-spray and cyclic tests conducted on a variety of precoated sheet products are reported. The precoated sheets were tested both with and without additional application of cathodically deposited electrophoretic primer. Results are compared to those for ordinary sheet steel coated only with primer and are discussed in terms of the degree of protection provided by barrier and galvanic mechanisms, as determined in separate electrochemical measurements. 13 ref.--AA