THE PREPARATION OF 7050 ALUMINUM ALLY ANODIZED FILM AND THE RESEARCH OF ITS MICRO ORGANIZATION

　　　Al and its alloy surface reacts with oxygen that can produce a layer of oxide film,the passive film can resist the atmospheric corrosion,but the alumina on the film is amorphous state and the film’s surface is uneven and discrete.Since the aluminium anodized technology appears, according to the classifications of electrolytes and external power supplies,there are so many types in the preparation technology of the aluminium anodized film,such as sulfuric acid method,oxalate method,organic acid method and DC method.This article firstly adopts the electrolytic polishing to process sample,then uses the two different mixed acids as the electrolyte and anodizes the aluminum alloy by Constant voltage DC,researches the effect of oxidation time on the growth thickness of aluminium anodized film,represents the micro structure of oxide film and analyzes the reasons why some phenomenons happened.

　　The experimental material is an as-cast 7050 aluminum alloy,its main chemical compositions(mass fraction,%) are 0.12Si,0.15Fe,2.0~2.6Cu,0.1Mn,1.9~2.6Mg,0.04Cr,5.7~6.7Zn,0.06Ti,0.08~0.15Zr.A metallographic sample of 10mm×30mm×10mm was cut on a block aluminum alloy,fine grinding on the waterproof abrasive paper of different types in turn,and rough polishing.Using a large concentration and particle size of Al203 powder mixed with water to make a coarse polishing agent, the revolution numbers of the polishing machine is 400～600r/min,do the appropriate elaborate polishing in the end,until the naked eyes can not see the obvious scratches.Wash with water,dehydrate with alcohol and dry for standby application.Eroding by a Keller reagent(mixed reagent with 1.0% HF,1.5%HCl,2.5%HNO3 and 95% of water)before electropolishing to display deformed layer.

　　70% of electropolishing solution (volume fraction) of 10ml of perchloric acid mixed with 90ml of anhydrous ethanol.Temperature is 80~90℃, voltage is 14～18volts,current density is 0.1A/cm² and polishing time is 20s.Stainless steel as a cathode in the experiment,firstly,take 7050 aluminum alloy samples into the HBF4 water solution to do the anode film and wash the samples with water after electrolysis.And then clean the electrolytic products on the surface in the 1:1(volume fraction)nitric acid solutions.Finally,clean with ultrasonic and wipe dry with alcohol to prepare for film covering.The equipment of film covering is same with electrolytic polishing,voltage is 15～22volts,current density is 0.1A/cm²,in a room temperature,and time is 5s.Two film casting solutions are selected,the one is made by HBF4 water solution(add 5.5g H3BO3 with 15ml,20%~30% of HF to be fully dissolved to the clear solution) and 500mL of distilled water.The other is made by38ml, 95%~98%(volume fraction) of sulfuric acid,43ml,85%(volume fraction) of phosphoric acid and 19ml of distilled water.

　　According to the polarization curve of Al and its alloys to adjust the time and current density,it is found that the low voltage and small current density are better for electrolytic polishing.The thickness of the anodized film increases with time in a certain period of time.The surface of the membrane was analyzed by XRD components.The results show that the surface of the film contains amorphous and crystalline Al2O3.

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