Consideration of salt-corrosion fatigue for lightweight design and proof of aluminium safety components in vehicle applications

Abstract Most of the available knowledge regarding the influence of corrosion on fatigue strength exists for constant amplitude loading resulting in Woehler-lines. However, the fatigue behaviour under spectrum loading, resulting in Gassner-lines, and simultaneously repeated corrosion is an area that is seldom investigated. The present paper presents the current state of the art regarding salt-corrosion fatigue behaviour, especially under spectrum loading, for forged, cast and welded aluminium vehicle safety components of the material families 5000, 6000, 42000 and 43000. The results obtained allow the estimation of fatigue-lines in air as well as under corrosion conditions. While wet-dry cycles or continuous irrigation with 5 %NaCl reduce the fatigue strength under constant amplitude loading by about 50% in the high-cycle regime, under spectrum loading the decrease in fatigue strength is, however, about 20%. The lower strength reduction under combined spectrum loading and corrosion enables experimental durability proofs in air without corrosive media by either increasing the amplitudes by about 15% or by extending the length of the applied spectrum by a factor of 2 to 3 to compensate for the fatigue life reducing effect of salt-corrosion. The favourable behaviour under spectrum loading opens lightweight design options despite the existence of corrosion conditions.