Fatigue Resistance of Al-Cu-Li and Comparison with 7xxx Aerospace Alloys

Abstract

Al-Cu-Li alloys are of great interest for aerospace applications due to their good mechanical property balance, excellent corrosion resistance and reduced density. These alloys exhibit an increased resistance to fatigue in particular when compared to 7xxx alloys. The metallurgical parameters affecting the fatigue resistance of alloys AIRWARE (TM) 2050-T8 and 7050-T74 alloys are studied. Crack initiation and propagation is characterized by FEG-SEM and optical microscopy on open hole fatigue specimens. Initiation on different constituent particles or on slip bands is observed, depending on the stress level, in alloy 2050-T8, whereas only initiation on constituents is observed for alloy 7050-T74. The Paris law is obtained from crack growth rate measurements of long and microscopic fatigue cracks, as well as from inter-striation distance. The fatigue crack growth rate of alloy 7050-T74 is twice that obtained for alloy 2050-T8. The relative contribution of initiation versus propagation time in the fatigue life is analyzed.