Corrosion Rates of Steel, Zinc and Bi-Metal Couples in the Field and in Laboratory Environments

Automotive corrosion is a complex issue since a vehicle is comprised of many materials and different locations on the vehicle experience different corrosion environments. As a result, multiple corrosion mechanisms are encountered. Hence, development of an accelerated corrosion test for automobiles that correlates well to real world corrosion situations is a challenging task. Most corrosion tests currently used in the automotive industry were designed for corrosion of steel. With an increasing use of aluminum and magnesium alloys, galvanic corrosion becomes a critical issue. Applying corrosion tests designed for steel to evaluate galvanic corrosion of lightweight alloys could lead to erroneous conclusions since the acceleration factors for the two corrosion mechanisms may be very different. To better understand the impact of corrosion environments on different corrosion mechanisms, corrosion sensors have been installed on the rooftop and under body of a vehicle to measure general corrosion rates of steel and zinc as well as galvanic corrosion rates of aluminum/steel and zinc/steel couples. The vehicle was driven daily in the Detroit metropolitan area and corrosion rates were measured every 10 minutes over a one-year period. Corrosion rates for the same materials were also measured in cyclic laboratory tests under various salt loads. Analysis of such data can lead to development of laboratory corrosion tests that shown improved correlation to real world corrosion situations.