Investigating the Benefits of Controlled Shot Peening on Corrosion Fatigue of Aluminium Alloy 2024 T351

Author:  Curtis, de los Rios, Rodopoulos, Romero, Levers
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002035
Year of Publication:  2002
Authors Sean A. Curtis 1, Eduardo R. de los Rios 1, Chris A. Rodopoulos 1, Jose Solis Romero 1, Andrew Levers 2 1 University of Sheffield, Sheffield, UK - 2 Airbus UK, Chester, UK Introduction It is widely accepted that the use of controlled shot peening (CSP) can be a beneficial process to improve the performance of metallic components. More precisely, it is recognised that it can increase fatigue life and reduce susceptibility to stress corrosion cracking (SCC), improvements generally accredited to the induced compressive residual stress layer close to the surface of the shot peened material. These two improvements due to CSP have been reported to be the most commonly investigated [1]. On searching the available literature, works on the effects of CSP on corrosion fatigue are far less in abundance. In most cases CSP was shown to increase corrosion fatigue life by introducing an effective compressive residual stress layer, which reduces crack propagation rates during the early stages of crack growth [2-7]. In one case, CSP was said to have had a greater effect at higher stress levels in a spring steel [8], whilst it has also been shown that the largest gain was achieved at lower stress levels in a structural steel [9]. However, contrary to the aforementioned results, evidence has been presented that shows no advantageous effect of CSP, in either a spring or structural steel, under corrosion fatigue conditions [10]. Possibly due to the mechanical nature of the fatigue phenomenon, very little attention appears to be directed towards the electrochemical effects of CSP. In [3], CSP was seen to have no effect on the free corrosion potential, Ecorr, in a 1.0N H2SO4 solution, but the corrosion current density, Icorr, was said to increase with peening. However, in a 3.5% NaC1 solution, Ecorr was seen to be nobler and Icorr was reduced. These latter findings are consistent with results observed in [11]. The present investigation has been made as part of an ongoing study into the effects of CSP. Aluminium alloy 2024 T351 is commonly used within the aerospace industry, and is routinely shot peened as part of the manufacturing process. To determine the effects of CSP on the corrosion fatigue behaviour of this alloy, a series of tests were performed. Initially, corrosion fatigue tests were conducted on both unpeened and peened specimens. Electrochemical testing was then undertaken, firstly, to investigate if the shot peening would change the characteristics of the material, and secondly, to help with the interpretation of the corrosion fatigue results.

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