How to Get Black Anodized Aluminum Strip

Anodic oxidation is the electrochemical oxidation of metals or alloys. Aluminum and its alloys form an oxide film on aluminum products (anode) under the action of external current under corresponding electrolytes and specific process conditions. Anodizing usually refers to sulfuric acid anodizing unless otherwise specified.

Coloring principle

The chemical coloring of aluminum anodized films is based on the adsorption capacity of the porous film layer. Generally, the diameter of anodized pores is 0.01-0.01um, while the dye is separated into single molecules in water with a diameter of 0.0015-0.0030um.

Coloring is when the dye is adsorbed on the pore surface, diffuses and accumulates into the pores, and performs ionic and hydrogen bonding with aluminum oxide to color the film. After the pore sealing treatment, the dye is fixed in the pores. There are rich colors for you to choose from like black, silver, red and so on. That’s how we get the black anodized aluminum strips.

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Anodizing sealing process

1. High temperature water sealing

This method uses the hydration reaction of the aluminum oxide film and water to change the amorphous film into a hydrated crystalline film. The hydration reaction can be carried out at both normal and high temperatures, but at high temperatures, especially at the boiling point, the hydrated crystal film generated is a very stable and irreversible crystal film.

2. Inorganic salt sealing

The inorganic salt method can improve the fastness of organic coloring dyes, so it is commonly used in chemical coloring methods. There are two methods: acetate method and silicate method.

3. Organic sealing method

This is to immerse the aluminum oxide film in oil, paint or Coating. Due to the high cost and increased process flow, it is not commonly used.

Coloring process

1. The anodized film can develop natural color

During the electrolysis process, parameters are adjusted to oxidize aluminum alloy elements, such as FE, Mn, etc., and then metal salts or other acids are added to the bath liquid to develop the color of the oxide film.

2. Electrolytic coloring

The bath liquid for electrolytic coloring is mainly Ni salt, Sn salt, Ni-Sn mixed salt. Others with industrial applications include Fe, Mn, Cu salt, etc. The color is still mainly light tones, and dark colors include bronze, maroon, etc. However, the color of electrolytic coloring is very stable and light-resistant.

3. Dyeing method

It is also necessary to obtain such a porous membrane layer. After cleaning, put it directly into the bath containing dye to allow the dye to adsorb on the hole wall.

This requires a high enough porosity and a certain adsorption activity on the inner wall of the pores. Therefore, more work is done on sulfuric acid oxidation film. The film pores of sulfuric acid oxidation film are relatively large and the color is relatively transparent, making it easier to obtain a purer dyed film.

After we get the desired anodized aluminum sheet, it can be slit into right specifications according to the customer requirements like aluminium strip 50mm x 2mm.

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