Corrosion behavior of 2099 Al-Li alloy in NaCl aqueous solution

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The corrosion behavior of 2099 Al–Li alloy in NaCl aqueous solutions with different concentrations (1.5, 3.5, and 5.0% in mass fraction) was investigated. Its corrosion resistance was evaluated using electrochemical measurements together with full immersion tests. The results showed that the 2099 Al–Li alloy possessed good corrosion resistance in NaCl aqueous solutions. Its corrosion rate increased with increasing chloride ion concentration. The main form of corrosion failure was pitting corrosion. The impurity containing sulfur leads to surface pitting. The oxide ﬁlms that formed during the manufacturing process offer a good resistance to corrosion. They are likely to suffer separation, cracking, and drop-off when immersed in aggressive NaCl aqueous solution. The good corrosion susceptibility of the alloy may be attributed to homogeneous coherent nanoscale precipitates.

I. INTRODUCTION

Reducing structural weight is one of the most important goals for the improvement of the aircrafts’ performance. Due to their low density and high strength, lower manufacturing and/or life cycle costs, aluminum alloys are particularly suitable for lightweight applications and have been the most widely used structural materials in aircrafts for several decades.1 Compared with the other aluminum alloys, aluminum–lithium (Al–Li) alloys exhibit higher elastic modulus, lower density, improved corrosion resistance, better fatigue performance, and higher speciﬁc strength. Nowadays, application of Al–Li alloys in the aerospace industry as structural components has become an important method to reduce the weight, increase the payload, and improve the fuel efﬁciency of aircraft.2 The signiﬁcant potential for weight savings has promoted the development of a series of Al–Li alloys.3 As one of the newly developed Al–Li alloys, the 2099 alloy can be considered as a promising aluminum alloy for aeronautical applications that involve lowest structural weight, highest damage tolerance and durability. 2099-T83 extrusion products have been qualiﬁed for use on Airbus A380 (Toulouse, France) applications such as crossbeams, seat rails, false rails, cockpit, fuselage skin, emergency bay ﬂoor structures, and electronic racks.4 It has been acknowledged that good corrosion resistance of aluminum alloys is attributed to the formation of a layer of rapidly formed passive oxide ﬁlm on surface. The oxide ﬁlm is naturally self-renewing, and accidental abrasion or other mechanical damage to the surface ﬁlm is rapidly repaired.5 However, in the presence of aggressive halide Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.121 J. Mater. Res., Vol. 29, No. 12, Jun 28, 2014

http://journals.cambridge.org

II. EXPERIMENTAL A. Specimens preparation

Commercial 2099-T83 alloy sheet with a thickness of 2 mm was used in this study. In the T83 state, the alloy was hot-extruded, heat-treated, tempered, and subjected to a 3% cold working before a two-step aging. Its nominal

a)

1344

anions, especially chloride ions (Cl), alumin

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