On the Anodic Oxidation of Aluminum Surface Treatment

Aluminum surface treatment is a series of mechanical and chemical surface pretreatment processes in the surface filming process with the mix and combination. Aluminum surface pretreatment methods are mechanical and chemical (or electrochemical) method two categories. Mechanical methods include sandblasting, brushing, wiping and polishing; chemical methods include degreasing, caustic washing, matte processing. Aluminum surface filming technology mainly anodic oxidation, chemical conversion, electroplating and electroless plating and organic coating.

  Closed process:

      Aluminum oxide film is a porous film, whether or not there is no coloring treatment, should be closed before processing, so as to improve its corrosion resistance and weatherability. There are three ways to deal with, that is, high temperature hydration reaction closed, salt and organic closed organic closed.

(1) high temperature water closed

         This method utilizes the hydration reaction of an aluminum oxide film with water to change the amorphous film into a hydrated crystalline film: the hydration reaction can be performed at normal temperature and high temperature, but at high temperature, especially at the boiling point, Hydrated crystalline film is a very stable irreversible crystalline film, therefore, the most commonly used anodized aluminum film is closed by boiling water method or steam treatment.

(2) salt closed

        Inorganic salt method can improve the fastness of organic coloring dyes, it is commonly used in chemical coloring.

        ① acetate method

       ② silicate method

(3), organic closed method

          This is the aluminum oxide film immersion oil, varnish or paint, etc., due to the higher cost and increase the process, it is not used, more or use the aforementioned two types of methods, and the first high temperature Water law as the mainstream.

          For aluminum-magnesium alloy oxide film is easy to generate, the quality of the film is better, can be oxidized, which is the difference between the alloy with an important feature; but in comparison, there are some shortcomings.

   The first point:

             Anodic oxide film with dual nature, and the larger pores, uneven distribution, it is difficult to achieve the best anti-corrosion effect;

   Second point:

              Magnesium has hardened and brittle, reduce elongation, increase the tendency of thermal cracking, such as ADC5, ADC6, etc., in the production, because of its wide range of solidification, shrinkage tendency, often produce shrinkage and cracks