Neue Ansätze zur Bewertung des Korrosionseinflusses auf die Schwingfestigkeit von Aluminiumlegierungen

Aluminium components are subjected to corrosive loadings during their service life in automotive vehicles, especially in the winter months due to the use of de-icing salts. Considerable amounts of localised corrosive damage in the form of pitting corrosion and intergranular corrosion can form over a period of several years to decades. Additionally, the combination of mechanical stresses and a corrosive environment leads to corrosion fatigue. This thesis therefore investigates the effects of corrosion on the fatigue behaviour of aluminium components. For a simultaneous mechanical and corrosive loading utilizing a 5% NaCl solution, it can be demonstrated that both investigated alloys, the high-pressure die-casting alloy AlSi10MgMn (EN AC-43500) and the wrought aluminium alloy AlSi1MgMn (EN AW-6082 T6), show a reduction in fatigue strength of 26%¿39% at 10^6 load cycles due to corrosion fatigue. No long-life fatigue strength limit under corrosion fatigue can be found up to a maximum number of load cycles of 10^7. The investigations on the high-pressure die-casting alloy AlSi10MgMn show that the reduction in fatigue strength is independent of the investigated surface conditions. A comparable reduction in fatigue strength of up to 37% at 2·10^6 load cycles was found for both the rough unmachined surface and the polished machined surface. The tests on the wrought aluminium alloy AlSi1MgMn reveal that the damaging effect of corrosion fatigue depends on the stress gradient. A significant increase of the support factor under corrosion fatigue conditions is shown for both pure tensile/compression and rotary bending loading. The combination of a reduced fatigue strength due to corrosion fatigue with a conventional support factor model based on tests in air leads to a conservative fatigue design assessment. S¿N tests of the two cast alloys AlSi9Cu3 and AlSi10MgMn in the pre-corroded state demonstrate a significant influence of localised corrosive damage on the fatigue strength. The long-life fatigue strength decreases by up to 42% depending on the depth of the corrosive damage. The fatigue strength of the pre-corroded samples is assessed utilizing fracture mechanical methods and measured material-specific parameters on the basis of a measured statistical corrosion depth distribution. The implementation of a short crack growth model has proven to be essential for a high-quality assessment.