Study On Preparation Of The Environment-friendly Anodization Of Aluminum Alloy And Mechanical Properties Of The Film

Aluminum,a non-ferrous metal material,is one of the most widely used metal materials.It presents light weight,high strength and other excellent properties which plays an important role in aerospace,transportation,civil construction industries and other fields.However,the mechanical properties of aluminum alloy(hardness,fatigue properties,wear resistance,etc.)is not ideal for its further application.Hence,it is usually anodized in an acid solution to produce an oxide film.This study use the 2024 aluminum alloy as substrate,anodizing in DC power mode in environment inorganic-organic electrolyte system(sulfuric acid-malonic acid).The effects of various process parameters(sulfuric acid volume ratio,oxidation temperature,reaction time,additive)and silanization treatment on the surface mechanical properties and corrosion resistance of 2024 aluminum alloy anodic oxide films were investigated.1.In the sulfuric acid-malonic acid system,under the conditions of oxidation current density of 3A/dm~2,the oxidation temperature(5~40?),the sulfuric acid volume ratio(4~10vol.%),the reaction time(50~120min)and the concentration of the inorganic additive(manganese sulfate:0.5~4g/L)are varied,and the effect of different process parameters on its surface properties are studied.The results show that under the different process conditions,the surface of the oxide film presents nano-sized pores and is connected by small units.The temperature factor has a great influence on the surface pore structure of the oxide film,when the temperature is higher than 25?,the pore size of the oxide film becomes larger with irregular arrangement of the pore structure,and the pore structures are destroyed while the temperature continues to increase.The optimized process conditions are:the temperature is 10?,sulfuric acid volume ratio is 10vol.%,the reaction time is 60min.Under this condition,the performances of the oxide film are:the thickness is 50?m,the microhardness is655.9HV,the friction coefficient is 0.324 with minimal wear rate,the load-displacement curves of the oxide film include three stages of loading,loading and unloading with nano-hardness of 4.836Gpa and the elastic modulus of 93.467Gpa,the corrosion current density is 1.265E-7A/cm~2,the roughness is 0.629?m.The thickness of the oxide film increases with the reaction time.When anodized for120min,the oxide film thickness can reach to 102?m.The microhardness changed obviously with the increase of temperature.When the temperature is higher than 25?,the microhardness decreased significantly,and the maximum of the microhardness is obtained at 10?.2.The anodic oxide film-organosilane film composite membrane are prepared by silylation treatment using KH-550,and the oxide film is formed under the optimized condition.The influences of the different silanization process conditions(silane volume ratio,silane hydrolysis time,silane hydrolysis temperature)on the wear resistance and corrosion resistance of the composite membrane are discussed.After silanization treatment,the film surface become more uniform with decreased surface roughness,and the wear resistance and corrosion resistance enhanced significantly.The optimum conditions for the silanization process are:the silane volume ratio is2vol.%with the silane hydrolysis time of 48h and the silane hydrolysis temperature of30?.Excessive silane volume ratio,silane hydrolysis time and silane hydrolysis temperature will lead to appearance of cracks on the composite film surface,which is not conducive to surface performance improvement.The wear mass and friction coefficient of the composite film are obtained the lowest value,which are 0.00056g and 0.098,respectively,when KH-550 hydrolyzed to 48h.The friction coefficient decreased by 69.75%and the wear mass was reduced by 11.67%,comparing to the non-silanized film.3.The effects of the sulfuric acid volume ratio and reaction time on the fatigue performance of the 2024-T4 aluminum alloy are investigated.The fatigue performance of the anodized specimen has declined.The thinner the oxide film,the better the fatigue performance.The optimum conditions for fatigue test are:the sulfuric acid volume ratio is 10vol.%and the reaction time is 30min.The oxide film has thinnest thickness(5~6?m)as well as the lowest fracture rate,and the number of fatigue fracture is the closest to the specimen without anodic oxidation.Under different oxidation conditions,the fracture micro morphology of the fatigue specimens are divided into the fatigue source area with 1~2 crack sources,the fatigue extension area without fatigue bands and smooth structure,and the instantaneous fault area in which the area of the dimple is clearly visible.The source region is basically based on quasi-cleavage.