T6态2090 Al-Li合金在EXCO溶液中的剥蚀行为和剥蚀发展过程中的电化学阻抗谱

采用电化学阻抗谱（EIS）和光学显微镜原位观察等方法研究了T6态峰时效的2090 Al-Li合金在EXCO溶液中的剥蚀行为.在浸泡过程中局部腐蚀形态演变经历了4个阶段：点蚀、晶间腐蚀、剥蚀和剥蚀后期.在点蚀阶段形成的以杂质相为局部阴极生成的大蚀孔成为剥蚀引发的中心,剥蚀鼓泡沿大蚀孔边缘生长,直到把表层以下完全穿透.点蚀引发阶段的EIS由一个高频容抗弧和一个中低频感抗弧构成,在点蚀发展阶段感抗弧消失.晶间腐蚀阶段的EIS的容抗部分中很难分辨出腐蚀区域对应的时间常数,剥蚀发展阶段和剥蚀后期的EIS由两个容抗弧构成.

EXFOLIATION CORROSION BEHAVIOR OF T6 TREATED 2090 Al-Li ALLOY IN EXCO SOLUTION AND EIS DURING EXFOLIATION CORROSION EVOLUTION

Electrochemical impedance spectroscopy (EIS) and in situ microscopic image of T6 peak-aged AA2090 Al-Li alloys in EXCO solution were studied. The localized corrosion form of the alloy during immersion evolved from pitting through intergranular corrosion, exfoliation corrosion (EC) to post EC. EC initiated at big corrosion pits which were formed with inclusion phase as center in pitting stage. The EC blisters propagate from these big pits till the upper layer is totally lifted. EIS of the initiation stage of pitting corrosion consists of a high frequency capacitive arc and a middlelow frequency inductive arc, and the inductive arc tends to disappear when pitting corrosion starts to propagate. In the intergranular corrosion stage, the second time constant corresponding to the corroded area can hardly be distinguished in the capacitive part of the EIS. In the stages of EC propagation and post EC, their EIS consist of two capacitive arcs.