Effect of Temper Condition on the Corrosion and Fatigue Performance of AA2219 Aluminum Alloy
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Effect of Temper Condition on the Corrosion and Fatigue Performance of AA2219 Aluminum Alloy Rahul Ghosh, A. Venugopal, G. Sudarshan Rao, P. Ramesh Narayanan, Bhanu Pant, and Roy M. Cherian (Submitted July 19, 2017; in revised form September 27, 2017) The effect of temper condition and corrosion on the fatigue behavior of alloy AA2219 has been investigated in different temper conditions (T87 and T851). Corrosion testing was performed by exposing the tensile specimens to 3.5% NaCl solution for different time periods, and the corrosion damage was quantified using a 3D profilometer. The exposure-tested specimens were subjected for fatigue testing at different stress levels, and the reduction in fatigue life was measured along with detailed fracture morphology variations. The results indicated that the alloy in both tempers suffers localized corrosion damage and the measured corrosion depth was 120 and 1200 lm, respectively, for T87 and T851 conditions. The loss in fatigue strength was found to be high for T851 (67%) when compared to that of T87 temper condition (58%) for a pre-corrosion time of 15 days. In both cases, fatigue crack initiation is associated with corrosion pits, which act as stress raisers. However, the crack propagation was predominantly transgranular for T87 and a mixed transgranular and intergranular fracture in the case of T851 temper condition. This was shown to be due to the heterogeneous microstructure due to the thermomechanical working and the delay in quench time imposed on the alloy forging in T851 temper condition. The findings in this paper present useful information for the selection of appropriate heat treatment condition to facilitate control of the corrosion behavior which is of great significance for their fatigue performance. Keywords
AA2219, fatigue, pitting corrosion, polarization
1. Introduction AA2219 aluminum alloy possess high strength, good weldability and stress corrosion cracking resistance which is being used in the aerospace industry for the fabrication of cryogenic propellant tanks (Ref 1-4). However, susceptibility to localized corrosion has been a drawback for this alloy especially in chloride containing environments. This was shown to be due to the presence of Cu and Fe containing intermetallic phases such as CuAl2 and Al7Cu2Fe which causes severe localized corrosion due to the formation of galvanic cells between those cathodic phases and the matrix aluminum (Ref 5-8). Localized corrosion such as pitting has been reported to be the major damage mechanism affecting the structural integrity of materials used in the aerospace industry (Ref 911). These pits act as stress concentrators initiating the fatigue cracks under the presence of dynamic loading which causes drastic reduction in fatigue lives of high-strength aluminum alloys such as AA2024 and AA7075. Duquesnay et al. Ref 12 examined the fatigue strength of AA7075-T6511 aluminum alloy after exposing to EXCO solution for different time periods and obtained severe reduction in fatigue
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