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Sealing of Aluminum Alloy Oxide Film

Release time:

2021-10-14 13:14

1. Definition of aluminum alloy oxide film sealing

The physical or chemical treatment process of the oxide film after aluminum anodic oxidation to reduce the porosity and adsorption capacity of the oxide film, so as to seal the dye in the micropores and improve the corrosion resistance and wear resistance of the film. In the construction industry, the sealing of the oxide film in the world basically adopts three processes: high temperature steam method, cold sealing and electrophoretic coating method, but the current medium temperature sealing has a tendency to expand. From the sealing principle, there are three main categories: hydration reaction, inorganic filling or organic filling.

2. Heat sealing hole process

A. boiling water sealing: in pure water close to the boiling point (temperature above 95 degrees, deionized water), amorphous alumina is converted into hydrated alumina through the hydration reaction of alumina. because hydrated alumina is 30% larger than the original volume, the volume expansion makes the micropore filling of the oxide film closed.

B. high temperature steam sealing: the principle and boiling water sealing, advantages: fast, water quality dependence is small, less white ash, fading risk is small. The equipment needs to be sealed to ensure temperature and humidity, the general temperature is 115~120 degrees, the pressure is 0.7 ~ 1atm, and the cost is high!

3. Cold sealing process

Cold sealing hole is the most commonly used basic sealing technology in our country. The operating temperature is 20~25 room temperature, the time and heat sealing hole ratio are shortened by half. It is sealed by the deposited filler in the micropores. The most mature process is the cold sealing process with nickel fluoride as the main component. After the cold sealing hole is completed, hot water aging (26-30 degrees deionized hot water, 10-15 minutes) is carried out to modify the product to avoid high temperature micro-cracking.

4. Medium temperature sealing process

In view of the defects of hot sealing and cold sealing process, the inorganic salt medium temperature sealing technology was developed, including chromate sealing, silicate sealing and acetate sealing.

A. chromate sealing: can provide good corrosion resistance, especially for die casting aluminum alloy and high copper aluminum alloy (PH6.32 ~ 6.64, about 10min)

B. silicate sealing: due to the silicate sealing often occur after lime or discoloration, at present, unless special needs do not use this process

C. nickel acetate sealing: sealing quality is better, used more in North America, our country in addition to organic dyeing of small parts, other basic not.