Study On Nickel Free Sealing Process Of Anodic Oxidation Of Aluminum Alloy

Anodic oxidation of aluminum alloy is a common surface treatment technology.The anodic oxidation of aluminum alloy has a large number of microporous structure units on the surface,which makes the aluminum alloy more prone to corrosion and damage in the natural environment.Therefore,it is particularly important to close the anodic oxidation film of aluminum alloy after anodic oxidation to reduce the porosity and adsorption capacity of the anodic oxidation film.The aluminum alloy oxide film sealed by the traditional sealing methods of dilute chromic acid,dichromate and nickel salt has good corrosion resistance,but the discharged wastewater contains Cr⁶⁺and Ni²⁺which pollute the environment and is harmful to human health.It is particularly important to develop a nickel-free sealing process to replace hexavalent chromium and nickel salt sealing.（1）1016 aluminum alloy was selected as the research object and anodized by sulfuric acid electrolyte.The influence of K₂Zr F₆concentration,CH₃COOLi concentration,additive A concentration and sealing time on the corrosion resistance of anodic oxidation film of aluminum alloy was analyzed at 25℃.The best closed formulations obtained were K₂Zr F₆concentration 20 g/L,CH₃COOLi concentration 7g/L,and additive A concentration 2 g/L.The optimal closure time is 12 min.In temperature 25℃,under the condition of closed time 12 min,the enclosed sample formula,its weightlessness eta is 21.2 mg/dm²,less than 30 mg/dm²,corrosion resistance in accordance with GB/T 87532-2005 standard.The zirconium and lithium seal was compared with the traditional boiling water seal and nickel salt seal.The zirconium and lithium seal oxide film had better corrosion resistance than the traditional boiling water seal and nickel salt seal.According to SEM analysis,the anodic oxide film of aluminum alloy was sealed with zirconium and lithium salts,and the surface had a dense sealing film,which had a good sealing effect on the porous structure of the oxide film surface.（2）The anodic oxidation of 1016 aluminum alloy was carried out by sulfuric acid electrolyte.By changing the concentration of K₂Zr F₆,the concentration of Cr（OH）SO₄,the concentration of additive M,the concentration of additive N,and the sealing time at 25℃,the influence law on the corrosion resistance of anodic oxidation film of aluminum alloy was analyzed.The best closed formulations obtained were:K₂Zr F₆concentration 10 g/L,Cr（OH）SO₄concentration 3 g/L,additive M concentration 0.7g/L,additive N concentration 0.35 g/L.The optimal closing time is 10 min.In temperature 25℃,10 min under the conditions of closed time,use the recipe closed1016 aluminium alloy,its weightlessness eta is 16.5 mg/dm²,less than 30 mg/dm²,corrosion resistance in accordance with GB/T 87532-2005 standard.The zirconium and trivalent chromium salt sealing was compared with traditional boiling water sealing and nickel salt sealing.The corrosion resistance of zirconium and trivalent chromium salt sealing oxide film was better than that of traditional boiling water sealing and nickel salt sealing.According to the SEM analysis,the anodic oxidation film of aluminum alloy is sealed by zirconium and trivalent chromium salt,and the surface has a dense sealing film layer,which plays a good sealing effect on the porous structure of the oxide film surface.By EDS film analysis,it can be concluded that zirconium and trivalent chromium salt seal film is composed of C,Cr,F,Al,S,O and Zr elements.The presence of C,Cr,F and Zr indicates that additives M,N,potassium fluorozirconate and basic chromium sulfate act on the anodic oxidation film of aluminum alloy and play a good sealing effect.（3）The properties of zirconium and trivalent chromium salt sealing solution were investigated.Chemical reaction occurred between zirconium and trivalent chromium salt sealing solution and the colorant used in the industrial production,which resulted in the discoloration of 1016 aluminum alloy after coloring by the sealing solution,indicating that the sealing solution was not suitable for the coloring agent used in the paper.The corrosion resistance of 1016 aluminum alloy sealed with zirconium and trivalent chromium salt seal solution was improved.Pure water,tap water,ultrapure water allocation zirconium,trivalent chromate sealing fluid closed weightlessness eta1016 aluminum alloy were 17.1,28.6,16.5 mg/dm².The sealing effect of zirconium and trivalent chromium salt in tap water is obviously reduced,while the sealing effect of zirconium and trivalent chromium salt in purified water is close to that of zirconium and trivalent chromium salt in ultra-pure water.The temperature range of zirconium and trivalent chromium salt sealing solution for purified water is wide,and the corrosion resistance of 1016 aluminum alloy sealed with the sealing solution conforms to GB/T 87532-2005 standard within the range of 9～32℃.The loading capacity of zirconium and trivalent chromium salt sealing solution is relatively large.The sealing solution can seal 1016 aluminum alloy oxide film with the area of 60 dm²for 1 L of pure water.When the sealing solution closes 1016 aluminum alloy oxide film with the area exceeding this value per liter,the sealing solution needs to be adjusted.The water allocation zirconium,trivalent chromate sealing fluid has a good stability,after 30 days of zirconium,trivalent chromate sealing fluid closed 1016 aluminum alloy,weightlessness eta,the largest is 26.3 mg/dm²,corrosion resistance in accordance with GB/T 87532-2005 standard.（4）The corrosion resistance of aluminum alloy oxide film 6063,3003,2024 and7075 with zirconium and trivalent chromium salt seal solution was improved.6063,2024,7075 aluminum alloy gravity eta were 20.4,23.7,24.5 mg/dm²,corrosion resistance are all accord with standard of GB/T 87532-2005,and 3003 aluminum alloy gravity eta is 42.5 mg/dm²,corrosion resistance do not accord with standard of GB/T87532-2005,the sealing fluid is suitable for 6063,2024,7075 aluminum alloy closed,do not apply to the 3003 aluminum alloy.According to the SEM analysis,the anodic oxidation film of 6063,2024 and 7075 aluminum alloy is sealed by zirconium and trivalent chromium salt,and the surface has a dense sealing film layer,which plays a good sealing effect on the porous structure of the oxidation film surface.By EDS film analysis,it can be concluded that zirconium and trivalent chromium salt seal 6063,2024 and 7075 aluminum alloy film layers are composed of C,Cr,F,Al,S,O and Zr elements.The presence of C,Cr,F and Zr indicates that additive M,additive N,potassium fluorozirconate,basic chromium sulfate and anodic oxidation film of aluminum alloy have a good sealing effect.