Optimierung von bruchmechanischen Kennwerten bei Aluminiumlegierungen für die Luftfahrtindustrie
Research output: Thesis › Doctoral Thesis
Cyclic loading occurs on a commercial jet airplane with each flight as the interior of the airplane is repeatedly pressurized and depressurized. Airplanes may see up to 100.000 pressurization cycles during their normal service lifetime. In many components therefore the resistance to crack formation under static and dynamic loading conditions is essential. Due to its attractive combination of high strength and damage tolerance material properties aluminum alloy AA2024 is the most important sheet material for aerospace applications. However this alloy is very susceptible to localized corrosion, which includes intergranular corrosion (IGC) and pitting corrosion. IGC is localized attack along the grain boundaries or adjacent to grain boundaries while the bulk of the grains remains largely unaffected. The resistance to IGC is mainly determined by the cooling rate to room temperature after solution heat treatment and by the grain size and grain shape. The aim of this work was to identify and improve those process parameters in the production chain of AA2024 T3 which are mainly responsible for good damage tolerance material properties. AA2024 sheet material in T3 temper with variations in grain size and grain shape was produced on industrial practice. A significant difference between globular fine grain and in-rolling-direction-elongated coarse grain material was investi¬gated with respect to intergranular corrosion resistance (IGCR) as well as fatigue crack propagation behaviour. The secondary precipitates present at the grain boundaries after solution heat treatment and water quenching are investigated by means of transmission electron microscopy (TEM). By using thermodynamic calculations the chemical composition of the alloy was optimized within the tolerance limits of AA2024 with regard to damage tolerance material properties. The heat treatment cycle of the rolling ingot homogenizing was adjusted to maximize the dissolution of the soluble Intermetallic precipitates. The adjusted chemical composition combined with the improved homogenizing has lead to a significant improvement of the toughness without impairing static mechanical properties. Further it was shown that through modification of the grain size and shape the fatigue crack propagation rate of AA2024 in delivery temper T3 can be further reduced. All these measures contribute to the reliability during utilization of aircraft components made of alloy AA2024.
|Translated title of the contribution||Optimization of fracture mechanical parameters of aluminium alloys for the aircraft industry|
|Publication status||Published - 2012|