Abstract
Anodized Aluminum alloys are widely used in aeronautic construction due to their specific mechanical properties. However, anodization process often leads to a decrease of the fatigue resistance of the alloys. In order to identify and characterize the different mechanisms involved in the detrimental effect of anodization of 2618-T851 alloy on its fatigue life and to determine the impact of loading nature, several tests have been performed on specimens with different surface states at various stress ratios. It was found that roughness of machining has no effect unlike the stress ratio or mean stress in tensile tests. The tests on the pickled, anodized, impregnated and sealed specimens showed it was the anodic oxidation step which was the more detrimental for fatigue resistance under tensile loading comparing to the other steps. It has been also observed that no such detrimental effect occurred under torsion loading. Concerning the prediction of fatigue life, two critical plane-based analysis approaches have been used (Morel and Fatemi-Socie criteria) to make fatigue life prediction for uniaxial and multiaxial fatigue test. Comparisons showed that both criteria gives overestimated fatigue life for uniaxial tensile loading under compression mean stress and underestimated fatigue life for tensile-torsion in phase loading.
Highlights
IntroductionIn many situations (especially in aircraft construction), it is necessary to modify the surface of previously machined parts by anodizing treatment to improve wear resistance and/or corrosion resistance of aluminum alloys [1]
In many situations, it is necessary to modify the surface of previously machined parts by anodizing treatment to improve wear resistance and/or corrosion resistance of aluminum alloys [1]
Fatigue tests have been performed for lives between 104 and 107 cycles in order to characterize the material parameters needed in the chosen multiaxial fatigue criteria
Summary
In many situations (especially in aircraft construction), it is necessary to modify the surface of previously machined parts by anodizing treatment to improve wear resistance and/or corrosion resistance of aluminum alloys [1]. Depending on aluminum alloy microstructure and pickling pre-treatment conditions, several pits could be produced due to galvanic coupling between intermetallic particles and aluminum matrix promoting the dissolution of intermetallic particles or surrounding aluminum matrix This creates surface defects acting as stress concentrators that promote the initiation of many small fatigue cracks and leads to fatigue resistance decrease [13, 14, 15, 16]. The fatigue resistance of anodized specimen is controlled by the crack initiation behavior in the substrate induced by the rupture of anodized film related to the deformation of substrate during fatigue process [17] From these various works on 2000 alloys series, it appears that the decrease of the fatigue resistance depends on the anodizing treatment, the loading nature and on the alloy itself. In terms of the microstructure, 2618-T851 alloy is characterized by the presence of many various intermetallic precipitates localized in grains and grain boundaries as shown in figure 2
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