Abstract
Intergranular corrosion is the main corrosion type of Al-Cu-Mg aluminum alloys, which seriously reduce the lifetime of aircraft structural parts. In this paper, the microstructure and the intergranular corrosion behavior of 2024 alloy with varying Cu and Mg content were studied by using a scanning electron microscope (SEM), transmission electron microscope (TEM), and three-dimensional atom probe (3DAP). The results show that nano-scale θ (Al2Cu) and S (Al2CuMg) particles precipitate along grain boundaries after quenching. The nano-cluster is the main strengthening phase in the 2024 alloy after natural aging for 96 h. The intergranular corrosion susceptibility is greatly affected by the presence of θ (Al2Cu) and S (Al2CuMg) phases along grain boundaries. Specifically, Cu-rich precipitates and intermetallics are known to act as local cathodes, which facilitates the action of oxygen reduction and ultimately drives anodic dissolution of the surrounding matrix material. The intergranular corrosion resistance of the alloy decreases with the increase in Cu and Mg contents. The alloy with a lower Mg content shows better corrosion resistance than the commonly used one with a Cu to Mg mass ratio of 2.9. The relationship between the observed corrosion behavior and various contents of Cu and Mg elements is discussed, which has potential to benefit the composition design of 2xxx aluminum alloy with high corrosion resistance.
Highlights
The rapid development of aerospace industry has put forward higher requirements for the comprehensive properties of Al-Cu-Mg aluminum alloy (2xxx series alloys), which requires high strength and toughness, and corrosion resistance [1,2]
All samples were exposed to the solutions (NaCl 30 g, HCl 10 mL, deionized water 1 L) at the temperature of 35 ± 1 ◦C for 24 h according to the Standard HB 5255
It is well known that the susceptibility to intergranular corrosion and to other localized corrosion is caused by the microstructure of the alloy
Summary
The rapid development of aerospace industry has put forward higher requirements for the comprehensive properties of Al-Cu-Mg aluminum alloy (2xxx series alloys), which requires high strength and toughness, and corrosion resistance [1,2]. Al-Cu-Mg aluminum alloys have wide applications in the aerospace industry due to their high specific strength, good fracture toughness, and excellent fatigue damage tolerance. Intergranular corrosion is one of the most serious reasons for the material failure of Al-Cu-Mg aluminum alloys as aircraft structural parts. Since the intergranular corrosion is not observed, it often causes sudden damage to structural parts. The detection of the incidence of intergranular corrosion is important from a maintenance perspective because it can develop into more severe forms of damage such as exfoliation, stress corrosion cracking (SCC), and fatigue cracking [6,7]
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