δ'相对铝锂合金常温电化学腐蚀行为的作用机制研究

Aluminum-lithium alloys,being among the lightest structure materials, are very attractive in the aviation and aerospace industries. Mechanical properies decreasing due to the electrochemical corrosion is the main failure reason of Al-Li alloy structures. It is well known that electochemical corrosion behavior has closely related to the number density, the size and the distribution of δ'phase in an Al-Li alloy. Our previous study results has showed that the electrochemical corrosion behavior of 2198 Al-Li alloy was different from 2024 Al alloy with Li-free. The cathodic process of 2198 alloy was controled by the oxygen and hydrogen evolution, while its of 2024 Al alloy was controled by the hydrogen evolution. δ' phase (Li) in 2198 Al-Li alloy could be participated in the passivation process. Alloyed element Li could be detected in the passive film, which could change the internal defect type of the passive film. The passive film containing Li formed on the 2198 Al-Li alloy had a p-type semi-conductor character and its without Li element had an n-type character. Thus, the electrochemical corrosion behavior of 2198 Al-li alloy could be changed due to the transformation from n type to p type. On the basis of our former work, double aging treament and Sc micro-alloy of Al-Li binary alloy were conducted in order to obtain the precipitation kinetics of δ' phase in this project. The electrochemical corrosion mechanisums of δ' phase in pitting corrosion, intergranular corrosion (IGC) and exfoliation corrosion (EC) were discussed from the testing results combinations of the conventional electrochemical testing, the surface analysis techniques and in-situ atomic force microscopy (AFM). Morover, the Sc rare earth effect on the electrochemical corrosion process was also discussed. This work has theoretical and practical significances to establish the relationship between the electrochemical corrosion behavior and microstructures of Al-Li alloy,thereby develop Al-Li alloys with high anti-corrosion and high mechanic performances.

铝锂合金是航空航天领域中最有竞争力的结构材料，其失效常是电化学腐蚀引起的力学性能下降，合金中δ'相的形态和分布对其电化学腐蚀起着至关重要的作用。本课题组前期研究结果表明2198铝锂合金阴极过程由析氢和吸氧共同控制，而不含Li的2024铝合金阴极过程由吸氧控制，原因是δ'相(合金元素Li)参与钝化膜形成过程且存在于钝化膜中，改变其内部缺陷类型(从n向p型转变)，从而影响腐蚀动力学。在此基础上本课题用双级时效和稀土Sc微合金化控制铝锂二元合金中δ'相的数量、尺寸及分布，采用常规电化学测试、表面分析和AFM原位观察相结合的技术深入研究常温水溶液环境中δ'相在点蚀、晶间腐蚀和剥蚀过程中的作用机制，加之探讨微合金Sc的稀土效应，该研究对确立铝锂合金腐蚀行为与微观结构之间的关系，开发具有高耐蚀性和高综合力学性能合金具有理论和现实意义。

真空熔炼制备Al-Li和Al-2Li-Sc合金，利用动电位极化、电化学阻抗(EIS)和Mott-Schottky曲线测量等电化学研究手段，结合X射线光电子能谱，阐明活性元素Li（δ'相）在Al-Li合金钝化和腐蚀过程中的作用机制，探讨稀土元素Sc对其腐蚀行为的影响。以力学性能作为评价标准，确定Al-Li合金时效制度，研究时效对Al-2Li合金在3.5%NaCl和EXCO溶液中的腐蚀行为。Li在降低合金热力学稳定性同时，加速钝化膜和腐蚀产物膜的形成。Li2O在膜表面的掺杂降低了膜中的载流子密度的同时能够提高膜的Fermi能级，是Li合金化提高Al耐蚀性的主要原因。不同热处理态Al-2Li合金耐蚀性由高到低的顺序为：20 h时效、固溶、40h时效和1h时效。在EXCO溶液中，时效使Al-2Li合金从固溶态的晶间腐蚀向剥蚀转变。0.5%Sc降低Al-2Li 合金的自腐蚀电位。该结果为建立Al-Li合金腐蚀行为与微观结构之间的关系提供实验指导，并为Al-Li合金的发展和应用提供理论依据。