Study On The Localized Corrosion Behavior Of Anodized New Type Aluminum-lithium Alloy

The advantages of the third generation Al-Li alloys include low density,high strength and toughness,as well as good fatigue performance.The third generation Al-Li alloys is widely used in aerospace industry.In aerospace industry,anodizing is used to improve the corrosion resistance of aluminum alloys.However,since intermetallic particles in Al-Li alloys often contain lithium and the lithium oxide is highly porous and soluble,under electric field and acid electrolyte.Therefore,voids arising from dissolution of intermetallic particles appear more frequently in Al-Li alloys.Previous work suggests an intimate correlation between particle-induced voids in the anodic filmand its corrosion resistance.However,the involved corrosion process and mechanism are still unknown.In this paper,the corrosion behavior of anodized Al-Cu-Li alloy AA2055 is investigated,with particular attention paid to intermetallic particle-introduced defects in the anodic film and the effect of such defects on corrosion behavior of the anodized alloy.The corrosion behavior of the anodized alloy was investigated through scanning electronic microscopy(SEM),transmission electron microscope(TEM),ultramicrocut,immersion test,electrochemical impedance spectroscopy(EIS),and glow discharge optical emission spectroscopy(GDOES).The main conclusions are as follows:(1)The major types of constituent particles in the solution-treated Al-Cu-Li alloy AA2055 are high-copper-containing Al-Fe-Mn-Cu particles,high copper Al-Cu particles and low copper Al-Cu particles which evenly distributed in the matrix with their diameters varying from ?1 to ?3 ?m.(2)Intermetallic particles present in the solution-treated Al-Cu-Li alloy AA2055 were preferentially oxidized relative to the alloy matrix of the anodizing in a mixed solution of0.46 M sulfuric acid and 0.53 M tartaric acid,at 14 V and 37 °C;the oxidized particles then dissolved rapidly during the subsequent anodizing process,resulting in void defects in the anodic film.(3)When immersed in 3.5% Na Cl solution,localized corrosion was found to initiate and then propagate in the alloy substrate beneath the anodic film.It is found that localized corrosion tend to develop in the region where a void is present beneath the anodic film;additionally,the corrosion susceptibility of the anodized alloy is dependent of the location of the void within the anodic film,with the void near/at the film/alloy interface is more likely to cause localized corrosion in the anodized alloy.With further exposure,corrosion propagates in peripheral regions along the film/alloy interface,with corrosion product diffusion outward via pores in the anodic film.(4)For anodized Al-Cu-Li alloy AA2055,the barrier layer play a vital role in obstructing the penetration of corrosive electrolyte to alloy substrate and the porous layer have a limited effect on obstructing the penetration of corrosive electrolyte.