| The new type aluminum-lithium?Al-Li?alloys are widely used inaerospaceindustry,due to their low density,high specific strength and specific stiffness,improving the pay load and fuel efficiency of the aircraft.However,like other high strength aerospace aluminum alloys,theAl-Lialloys are susceptible to localized corrosion.In industry,the corrosion resistance of aluminum alloys is usually improved through anodizing treatments.Focused on the new type aluminum-lithium alloy AA2099-T8 and the new anodizing technology tartaric-sulphuric acid anodizing?TSA?,the corrosion resistance of the anodized alloy is studied.Additionally,the effects of temperature,concentration of tartaric acid and sealing treatment on corrosion resistance of the anodic oxide film are investigated.The following conclusions have been drawn from the work.1)Large numbers of second phase particles in AA2099-T8 specimens affect anodizing behavior and the structure of the anodic films.The oxidation velocity of the low-copper-containing Al-Fe-Mn-Cu-?Li?particle is slower than the matrix,but the film formed on it is continuous and compact.While the high-copper-containing particle dissolves rapidly during anodizing,resulting in defects in the anodic film.Such film defects provoke localized corrosion in the anodized alloy.2)As anodizing temperature rises,the film growth rate and total film thickness increased.When the temperature is higher than 37?,rod-shaped cavities with their distribution consistent with that of T1 phase appeared.Due to increased dissolution and film porosity,the corrosion resistance of the anodic film generally decreases with increase of anodizing temperature.3)The increased concentration of tartaric acid leads to lower film dissolution rate.The rod-shaped cavities associated with T1 phase become less evident and even disappear with increase of tartaric acid concentration.As the concentration of tartaric acid rises,the film growth rate and film thickness first increase and then decrease,peaking with 0.3 M tartaric acid addition.Due to decreased film dissolution and film porosity,the corrosion resistance of the anodic film generally increases with increase of tartaric acid concentration.4)After sealing anodic films in a lithium hydroxide solution at room temperature for a short time,platelet-like precipitates composed of LiH?AlO2?2·5H2O and hydrated alumina are formed on the surface.As a consequence of sealing,the Ecorr of the anodic film increased from-0.686 V to-0.464 V and the corrosion density decreased from 2.363×10-8 to 1.376×10-9A/cm2. |
PDF Full Text Request