Corrosion and Aging Behavior of 2A97 Al-Li Alloy with Typical Protective Coatings in Tropical Marine Atmosphere Environment

Two typical protective coatings applied on 2A97 Al-Li alloy were exposed in Wanning natural environment test station in Hainan island, and their corrosion and aging behavior were studied by means of surface and cross section morphology observation, infrared spectroscopy, electrochemical impedance spectroscopy and other methods. The 2A97 Al-Li alloy was firstly subjected to anodic oxidation treatment, then applying either two layer coating of primer+topcoat (coating 1) or mono layered coating of only primer (coating 2). The results show that after 2.5 a exposure, the coating 1 keeps intact i.e. the coating and anodized layer are relatively complete, and the alloy matrix is not corroded. In the contrast, a large number of micro cracks emerge in coating 2 after 1 a exposure, and even spallation can be ob served in some local areas of the coating, meanwhile, the anodic oxidation layer becomes thinner and the alloy matrix suffers from corrosion with the extension of exposure time. Compared with the coating 2, the coating 1 has better aging resistance, showing lower rate of light loss and chromatic aberration. The impedance spectrum of coating 1 consists of a capacitive reactance arc after different periods of exposure, which means that the corrosion process of coating 1 is mainly controlled by the inward diffusion of water and oxygen. While the electrolyte invades the interface between coating 2 and the matrix after 1 a exposure, and the coating begins to peel off with the extension of exposure time, which is mainly manifested as the corrosion of Al-Li alloy matrix, and the corrosion rate is controlled by the electrochemical process.