Effect of Aging State and Cu Content on Intergranular Corrosion Sensitivity of Al-Cu Alloy

The intergranular corrosion（IGC） sensitivity of Al-xCu alloys（x=0.54, 1.05, 2.10, 3.60, 4.50, wt%） with different effective states was investigated by hardness, accelerated corrosion, electrochemical measurements, scanning and transmission electron microscopy analysis. The results show that the low Cu alloy always has IGC sensitivity and the corrosion degree increases with the aging time increasing. The high Cu alloy first generates IGC, and is converted to steady-state pitting corrosion in the obsolete phase. Microstructure and electrochemical analysis show that the IGC of low Cu alloy originates from the formation of corrosion microbattery with grain boundary rich Cu layer and non-evolution zone（PFZs）, and the increase of corrosion degree is related to the increase of segregation degree in rich Cu layer. The IGC of high Cu alloys is derived from the formation of corrosion microbatteries with the PFZs of matrix and grain boundary precipitates. However, the grain boundary precipitates gradually change from continuous distribution to intermittent distribution during aging, which determine the change of corrosion behavior from IGC to steady-state pitting. Moreover, the steady-state pitting corrosion of high Cu alloys during the out-of-date effect stage is also related to the Cu crystalline phase and matrix composition.