Corrosion by biofuels - Protection by coatings also under cyclic loadings

The influence of corrosion on fatigue design must be considered in numerous component parts in the automotive industry. By using appropriate coatings the negative influence of corrosion under static and cyclic loading can be suppressed. Using the aluminum cast alloy AlSi7Mg0,3 T6 as an example, selected material-coating-systems were to be characterized under mechanical-thermal-corrosive complex loadings and characteristic properties for the fatigue design under cyclic loadings were to be determined. Conditioning tests were carried out with uncoated, anodized and chemical-nickel-plated specimen at different temperatures in the media fuel E5 (fuel with 5 % ethanol added) and E10 (fuel with 10 % ethanol added) and followed by SEM examined. The cyclic fatigue tests with chemically-nickel-plated and tempered aluminum in the fuel E5 at 100 degrees C no reduced influence on the fatigue strength, within the scattering, was discerned. This result agrees with the conditioning tests in the fuel E5 at 100 degrees C, where no corrosion was observed. Despite the coating of the specimens salt spray fog leads to a clear reduction in the fatigue strength. Using a damage accumulation calculation, it could be shown, that the real damage sum of the callipers and specimens, despite different types of coating, are comparable.