Chromium free oxidation of the five hottest alumin

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Chromium free oxidation of five aluminum alloys

chromium free oxidation of five aluminum alloys:

1. Immerse the aluminum alloy in boiling water, the natural oxide film of aluminum will continue to thicken, and finally reach 0.7 ~ 2 μ m。 The oxide film is colorless or milky white, and the water oxide film is γ Boehmite alumina has a dense structure and a very stable membrane at pH between 3.5 and 9. It can be used as the bottom layer of paint. Superheated steam above 100 ℃ is conducive to the formation of membrane. The actual process is to treat it in pure water at 75120 ℃ for several minutes. In order to improve the film thickness, ammonia or triethanolamine is added to pure water to obtain a porous oxide film. The color of the oxide film treated with ammonia water is white and uniform. The maximum addition range of ammonia is 0.3% - 0.5%

2. Zirconium salt oxidation method

zirconium containing solution has been accepted as a substitute for chromate for the pretreatment of aluminum base surface, which is especially suitable for the chemical conversion film treatment of aluminum alloy parts before coating, which can increase the adhesion between the coating and the substrate and improve the corrosion resistance. At the same time, the oxide film itself also has certain corrosion resistance

3 titanium salt oxidation method

titanium is very similar to chromium in nature and does not corrode in almost all natural environments. Its excellent corrosion resistance comes from the continuous, stable, firmly bonded and protective oxide film formed on its surface. Titanium's high reactivity and strong affinity with oxygen make its metal surface immediately form oxide film when exposed to air or humid environment. In fact, like chromate chemical oxide film, as long as there is a trace of oxygen or water (moisture) in the environment, the damaged titanium oxide film can immediately repair itself due to the strong affinity between titanium and oxygen

4 rare earth metal salt oxidation method

rare earth metal salt chemical oxidation film may replace chromate chemical oxidation film in the future. Materials can be treated by immersion method. The treatment solution generally needs to be heated to produce a protective layer on the surface of the base metal. Its corrosion resistance is provided by the formation of rare earth oxide worship on the metal surface. The surface area of this kind of 2-dimensional gold single crystal exceeds 104 square microns. At present, the rare earth treatment process of aluminum alloys generally adopts the treatment method of mixed solution composed of rare earth metal salts, oxidants, film-forming accelerators and auxiliary film-forming agents. Rare earth salts mainly refer to cerium salts, such as CeCl3, Ce (NO3) 3, Ce (SO4) 2, (NH4) 2ce (NO3) 6, etc., film-forming accelerators include NaOH, HF, SrCl2, (the world's latest graphene raw material preparation technology NH4) 2ZrF, which has been successfully studied by Johnson & Johnson for many years, and oxidants include H2O2, KMnO4, (NH4) 2S2O8, etc. The treatment process without oxidant in the treatment solution includes rare earth bohmite layer process. This process is to form a bohmite layer on the surface of the aluminum alloy with hot water, and then dip it into the rare earth salt solution to form a bohmite layer containing rare earth. The characteristic of this process is that strong oxidants such as H2O2 and KMnO4 are not needed to shorten the treatment time, but the treatment temperature is high

5 permanganate oxidation method

generally speaking, permanganate is not only a good corrosion inhibitor for aluminum and alloys, but also can accelerate corrosion. However, aluminum and its alloys can form a good protective film after proper treatment in KMnO4 solution. The process includes continuous immersion in sodium bromate, distilled water, Al (NO3) 3-lino3 solution and KMnO4 solution, and the composition of the obtained film is Al2O3 · MnO2. If k2SiO3 solution is used to seal the oxide film, the back and seat of the fine pore bench will be cured in the oven, and the effect will be better. The protection of KMnO4 oxide film is about 70% of that of chromate film (calculated in the same period of salt spray test). For pure aluminum and aluminum alloys with low copper, zinc or iron content, a uniform yellow film similar to that of chromate oxide film can be formed after treatment in potassium permanganate aqueous solution for 1 minute. For aluminum alloys with high corrosion tendency, in order to obtain a thicker protective film, it should first be treated in boiling water or steam to form oxidation worship, and then the film should be sealed for two or three times. One is to seal in aluminum salt, and the other is to seal in KMnO4 solution. The performance of the oxide film formed in this way can be compared with that of chromate film. For aluminum alloy with high copper content and without coating, in order to obtain the best protective film, a process of treating with 95 ~ 100 ℃ potassium silicate solution for 1.5min can be added, which is compared with that of chromate film, The biggest advantage of this film is that the point of promulgation of the two EU Directives "waste electronic and Electrical Equipment Directive" (WEEE) and "Prohibition of hazardous materials in electronic and Electrical Equipment Directive" (RoHS) is that the drying temperature exceeds 65 ℃ and long-term storage will not reduce its protection. Potassium permanganate oxide film and chromate oxide film have exactly the same protective performance against filiform corrosion under the paint film

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