The effect of combined shot-peening and PEO treatment on the corrosion performance of 2024 Al alloy

Mechanical fatigue can be a performance limiting factor for surface treated aluminium. A duplex treatment combining mechanical cold-work with a hard surface layer has been demonstrated to significantly improve the fatigue resistance compared to the results for a hard coating alone. A further consideration is that of corrosion resistance; Plasma Electrolytic Oxidation (PEO) can be used to reduce the susceptibility to corrosion whereas shot-peening is known in some cases to be detrimental, particularly if a ferrous peening media is used. In this work, the corrosion resistance of three different surface treatments (i.e. single shot-peening and PEO as well as their combination) is investigated on a 2024-T351 aluminium alloy. Corrosion studies were carried out in a 3.5% NaCl solution using open circuit potential and electrochemical impedance spectroscopy techniques. Surface microstructure and phase composition were studied by optical microscopy and XRD analyses, respectively. The effect of the duplex treatment is discussed in comparison with that of the single treatments and as-received (mill finish) surfaces. Shot-peening is seen to reduce the resistance to corrosion whilst PEO substantially improves it; the combination of the two provides a level of resistance comparable to that of PEO alone.