Influence of Mg Content on the Corrosion Behavior and Precipitation of Aged Al-Cu-Li-xMg Alloys

Aluminum (Al)–copper (Cu)–lithium (Li) alloys are susceptible to environmental degradation, which limits the in-service lifetime of the components. Because of their complex composition, there are seldom studies focusing on corrosion behavior influenced by one single element, which is essential to clarify the corrosion mechanism. Herein, the sole influence of Mg on the corrosion behavior of Al–Cu–Li–xMg alloys was analyzed. Results revealed that the addition of Mg can affect the nucleation and precipitation process of the T1 precipitate, resulting in a difference of potential between grain interior and grain boundary. The precipitation of the T1 precipitate was promoted in a 0.7Mg alloy while impeded in a 1.1Mg alloy, due to the competition of Cu atoms and nucleation sites between T1 and S′. Two types of corrosion behavior of Al–Cu–Li–xMg alloys appeared due to the potential difference and continuity of grain boundaries. Continuous precipitates in grain boundaries and less precipitates within the grain are likely to cause intergranular corrosion (IGC), while more precipitates within the grain will result in pitting.