Corrosion Performance and Fuel Compatibility of Prepainted Zinc-Nickel Coated Steel for Fuel Tank Applications 971006

Automotive demands for increased service life and use of flexible fuel blends of alcohol and gasoline have propelled the development of new materials for automotive fuel systems. Traditional fuel system materials, i.e., bare or prepainted terne coated steel sheet, which do not meet the new requirements are being replaced with prepainted zinc-nickel coated steel sheet. Automotive fuel tanks and fuel system components made from the new prepainted zinc-nickel steel sheet offer increased service life and compatibility with the entire range of flexible fuel blends.

This paper describes the results of several laboratory corrosion studies which examined the environmental corrosion performance and the fuel compatibility of prepainted zinc-nickel coated steel as a function of several system properties. Performance is compared to prepainted terne, prepainted hot dip tin, and prepainted galvanneal. Environmental corrosion performance was evaluated using the cyclic corrosion tests of Ford's Laboratory Simulated APG, General Motors 9505P, Cycle J, and General Motors 9540P, Method B, and the ASTM B117 salt spray test. Fuel resistance and compatibility of these materials was evaluated through six-month duration exposure tests to various flexible fuel blends at the elevated temperature of 60 °C. A number of different zinc-nickel painted samples were included in the program in order to determine the effects of zinc-nickel coating weight, pretreatment type, and paint thickness.

Results are described and analyzed in terms of the material's resistance to paint delamination and/or paint blistering, and in terms of substrate protection and delay in red rust formation at scribes, cut edges, and deformed areas. Analysis of results indicates that electroplated zinc-nickel steel sheet painted with an aluminum-rich epoxy provides the best overall fuel tank performance; second best was galvanneal sheet coated with a very similar paint system.