What is Aluminum Anodizing Process

  • Aluminum anodization is a type of metal surface finishing method and electrolytic oxidation process in which aluminum or aluminum alloy products are used as anodes and inserted into an electrolyte solution for treatment purposes, and the aluminum oxide film is formed by electrolysis, known as aluminum anodization (aluminum alloy). In this article, we will talk about the basics of the process of aluminum anodizing, covering the anodizing application, treatment process and development.

    Method for Aluminum Anodizing Application
    On the surface of aluminum, several micrometers and hundreds of micrometers of oxide film can be formed following anodizing. The corrosion resistance and the decorative properties are obviously improved compared to the natural oxide film of aluminum alloy. It is possible to anodize non-ferrous metals or their alloys (for example, aluminum, magnesium and their alloys). In CNC machining components, aircraft and vehicle parts, precision instruments and radio equipment, everyday necessities and architectural decoration, this technique is frequently used.

    Aluminum Surface Anodization Treament Phase
    Various degrees of dirt and defects on the surface, such as dust, metal oxidation, metal oxidation (natural or aluminum oxide film formed at high temperatures), residual oil, asphalt stains, manual handling of fingerprints (mainly consisting of fatty acids and compounds containing nitrogen), solvents, corrosion, can occur no matter what procedure is used to treat aluminum materials and products. It is also important to clean the surface of the product by chemical and physical methods before the oxidation treatment, which can clean the metal matrix and promote the smooth progress of the oxidation coloring. Therefore, it is possible to obtain an artificial film with the highest corrosion resistance, wear resistance and weather resistance.

    Degreasing The Degreasing
    On the surface of aluminum and aluminum alloys, organic solvent degreasing, surfactant degreasing, alkaline solution degreasing and acid solution degreasing are accessible. Electrolytic degreasing and degreasing of emulsions.

    Etchant of the Alkali
    Alkaline etchant is a surface cleaning procedure used with or without other substances for aluminum items in sodium hydroxide solution, which is also known as alkaline corrosion or alkaline cleaning. Its purpose is to remove the natural oxide film and a minor scratch on the surface of the product as a supplementary treatment after degreasing by some degreasing methods, so as to further clean up the oil dirt attached to the surface. Therefore, the product's pure metal matrix is exposed, which is conducive to anode film creation and high-quality film acquisition. Furthermore, it is possible to obtain smooth or satin matte or glossy etched surfaces by adjusting the composition of the solution, temperature, treatment period and other operating conditions. Sodium hydroxide, in addition to regulators (NaF, sodium nitrate), scaling inhibitors (gluconate, heptane, tartrate, arabic gum, dextrin, etc.), multivalent chelating agents (polyphosphate), and detergents are applied to the basic composition of the etching and washing solution.

    Neutralization and the cleaning of water
    The gray or black hanging ash on the surface of aluminum products may not dissolve in cold or hot washing water after etching and washing, but can dissolve in an acid solution. Therefore, to eliminate hanging ash and residual alkali solution, the products etched and washed by hot alkali solution must be cleaned by acid leaching in order to reveal the bright basic metal surface. This process is referred to as neutralization, treatment of luster or gloss. The method is to soak the substance at room temperature in a solution of 300-400g / L nitric acid (1420kg / m3). The soaking period varies with the composition of the metal. The time for soaking is usually 3-5 minutes.

    Hanging ash on silicon or manganese-containing aluminum alloy products can be treated for 5-15 seconds with a combination of nitric acid and hydrofluoric acid with a volume ratio of 3:1 at room temperature. A solution containing 300-400 g/L nitric acid and 5-15 g/L chromic oxide or a solution containing 100 g/L chromic oxide plus 10 ml/L sulfuric acid (1840 kg/m3) can also be administered at room temperature for neutralization therapy. In each process, the purpose of water cleaning is to thoroughly remove the residual liquid and water-soluble reaction products from the surface of the product in order to avoid contamination of the tank liquid during the next process and to ensure the efficiency and consistency of the procedure.

    Most of them have been washed once with cold water. However, after alkali corrosion, the items are normally washed with hot water, followed by cold water. The warm water temperature is 40-60 ° C. After water washing, the neutralized materials may be oxidized, so this cleaning should be especially careful in order to avoid the contamination of the clean surface. Otherwise, because of insufficient washing, the successful treatment of the previous processes could be lost. The surface should be oxidized with the solvent after neutralization and water washing. It should not be too long to stay in the air, such as remaining for 30-40 minutes, re-etching and neutralization of goods.

    Natural alumina is soft and thin on the surface of aluminum items, with low resistance to corrosion, which cannot be an efficient protective layer and is not appropriate for coloring. The artificial film of oxide is primarily developed by chemical oxidation and anodic oxidation. Chemical oxidation is a reaction in a weak alkaline or weak acid solution of part of the base metal of aluminum products that thickens the natural oxide layer on the surface or creates some other passive films. Chromic acid film and phosphoric acid film, which are thin and have good adsorption, and can be colored and sealed, are the popular chemical oxide films. Chemical oxidation film is much thinner compared to anodic oxidation film, with low resistance to corrosion and hardness, and it is not easy to paint, and the light resistance after coloring is weak, so the coloring and color matching of aluminum metal only introduces anodizing treatment.