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Corrosion Fatigue Crack Growth Rate Behaviour of AI2024-T3 in

Seawater Environment

ABSTRACT

Aluminium alloy 2024-T3 has been used in aircraft construction for many years because this alloy fidftls requirements for aircraft materials, i.e, it has high strength to weight ratio and gives cost- effective structure which is durable and damage tolerant at ambient, sub-zero and occasionally elevated temperatures. However, aluminium alloy 2024-T3 is susceptible to pitting corrosion when it is operated in corrosive environment such as seawater. Combined effect of dynamic load and corrosion attack on an aluminium alloy 2024-T3 structure will lead to corrosion fatigue damage. The present investigation aims to study the behaviour of corrosion fatigue crack growth rate of aluminium alloy 2024-T3 in seawater environment.

In this investigation, corrosion fatigue behaviour of aluminium alloy 2024-T3 was studied using constant amplitude fatigue experiments carried out in seawater environment with stress ratio (R) and frequency of 0.1 and 30 Hz respectively whereas specimens used were centre crack tension type. In addition, corrosion rate test was carried out using three electrode potential method using saturated calomel (HgjCIi) electrode (SCE) whereas the auxiliary electrode was platinum. The corrosion test was performed in seawater environment.

Results of this investigation shows that aluminium 2024-T3 in seawater exhibits passivity behaviour and higher potential typically above -750 mV may destroy passive film marked by a significant increase in corrosion rate. The fatigue crack growth rate (da/dN) of this alloy in seawater environment is higher than that tested in air in the region where stress intensity range, AK is higher than 20 MPa'im. Finally, mechanism in which corrosion affects fatigue crack propagation is proposed.

Keywords : Aluminium alloy 2024-T3, corrosion fatigue, seawater

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