The Influence of Different Aging Temperatures on the Microstructure and Corrosion Behavior Evolution Characteristics of the Al-Cu-Li Alloy

In the current work, the microstructural characteristics and corrosion performance of an Al-3.6Cu-1.0Li-0.40Mg-0.32Mn-0.12Zr alloy are correlated across different artificial aging regimes (150 °C, 160 °C, and 170 °C). In the under-aging stage, the corrosion depth increases with rising aging temperature, from 342.86 μm at 150 °C to 495.13 μm at 170 °C, indicating deteriorated corrosion resistance at higher temperatures. This trend is closely related to the significant increase in the proportion of the T1 phase in the matrix’s primary precipitate. Upon artificial aging for 24 h, the hardness increases gradually as the aging temperature rises. At higher aging temperatures, short-term aging hardness is higher, likely due to the formation of the T1 phase, which can also provide a strengthening effect. In contrast, the corrosion resistance of the alloy is enhanced at higher aging temperatures after 24 h of aging. These corrosion phenomena are closely related to the dominance of the θ″ phase during low-temperature aging and the gradual increase in the S′ phase during high-temperature aging. Furthermore, a transition from intergranular corrosion to pitting corrosion is identified at the high aging temperature of 170 °C with extended aging time. This corrosion mode transformation behavior is speculated to result from intermittent formation of magnesium segregation near the grain boundary, which alters the electrochemical heterogeneity between grain boundaries and the alloy matrix.