| With the continuous deepening of research on aluminum-lithium alloys,the application range of this material in the aerospace field is continuously expanding.However,due to the addition of Li,the mechanical properties and corrosion resistance of the material are changed.The surface of aluminum alloy is usually used in actual production.Oxidation treatment is used to protect the surface of the alloy and improve the surface properties of the alloy.However,there is no research on the aluminum-lithium alloy to systematically analyze the role of Li in the oxidation process of the alloy.This article aims to improve the oxidation protection of the aluminum-lithium alloy Performance to deeply explore the role of Li in the oxidation process of Al-Li alloy and its influence on the oxidation structure and performance.The research in this paper shows that:due to the addition of Li,evenly distributed fine pits appear on the surface of the oxide film.Both the concentration of the anodic oxidation sulfuric acid electrolyte and the Li content in the alloy promote the formation of the oxide film.Li at a concentration of 18%sulfuric acid The average thickness of the Al-Li alloy anodic oxide film with a content of 1.53%is the largest,reaching 64.7?m,The average thickness of the Al-Li alloy micro-arc oxide film with a Li content of 1.53%at a concentration of 0.05 mol/L sodium silicate is the largest,Reached 121?m.The outside of the anodic oxide film is a loose layer,and the inside is a dense layer.The surface of the film is distributed with fine micropores.With the increase of Li content and electrolyte concentration,the size of the micropores on the surface of the film expands and microcracks appear.Under the conditions,the corrugated structure appears.The main phase composition of the anodic oxide film is ?-A2O3,?-Al2O3 and Al2(SO4)3,which may contain LiH and Al.The oxide of LiH is LiOH,and the Al2(SO4)3 phase is in the oxide film.It is found in the dense layer,indicating that it has been formed in the early stage of oxidation.Li is distributed along the micropores of the oxide film and the Li content is lower on the side close to the electrolyte.The mechanical and corrosion resistance test results show that the macro Vickers hardness of the Al-Li alloy oxide film layer increases with the increase of Li content,up to 32.124HV,which is lower than the macro Vickers hardness of pure Aluminum,while Al-The microhardness of the Li alloy oxide film at 1000nm is most affected by the electrolyte concentration.The hardness of the oxide film at low electrolyte concentration is up to 1.25GPa,and the elastic modulus is up to 55.3GPa.With the increase of Li content,the corrosion resistance of the anodic oxidation and micro-arc oxidation coatings is in a downward trend,and the overall corrosion resistance of micro-arc oxidation is lower than that of anodic oxidation.The growth kinetic curve of Al-Li alloy anodic oxidation conforms to the parabolic law.Corresponding to the results of SEM and forward current,it can be seen that the oxide film mainly grows in the dense layer during the initial 5-10min,and fast growing fibrous can be observed on the surface of the dense layer ?-Al2O3 phase.The loose layer begins to form at 1520 minutes in the middle stage,and enters the steady state stage at 20-40 minutes.At this time,the loose layer of the oxide film becomes uniform and stable,which conforms to the morphology of the porous anodic oxide film.As the oxidation time decreases,the corrosion resistance of the oxide film decreases,and the corrosion current increases when the loose layer begins to form,indicating that the formation of the loose layer destroys the overall compactness of the oxide film,leading to the corrosion rate when entering the corrosion stage increase. |
PDF Full Text Request