Progress by the Automotive and Steel Industries Toward an Improved Laboratory Cosmetic Corrosion Test

A cooperative effort by the North American automotive and steel industries is being spear-headed by the Corrosion Task Force of the American Iron and Steel Institute (AISI). This work is aimed at development of an improved laboratory accelerated test for ranking the cosmetic corrosion resistance of automotive steel sheet products. In this paper, we review the AISI program including its objective, approach, and relationships with other organizations, particularly with SAE's Automotive Corrosion and Prevention Committee. Results of four cyclic laboratory tests considered by the Task Force are compared to those of two-year on-vehicle tests conducted in the severely corrosive environments of St. John's, Newfound-land and Montreal, Quebec. Statistical methods are used to depict the material rankings of each test, and to compare the rankings between the laboratory and field tests. Corrosion mechanisms in the AISI cyclic tests are described in terms of the mode of attack and corrosion products as determined by a variety of analytical methods. Although the AISI cyclic tests give a good correlation with scribe creep of coated sheet in the on-vehicle test, they underestimate the amount of scribe creep exhibited by cold rolled steel, thus indicating that further improvement is needed. Nevertheless, the AISI cyclic tests are much better than the ASTM B117 salt spray test which is shown to be totally unsuitable for ranking the cosmetic corrosion resistance of coated steel sheet products.