Oxidation process for aluminum

Pretreatment
1. Cleaning First of all, aluminum should be cleaned to remove oil, dust and other impurities on the surface. Alkaline solutions or special aluminum cleaning agents are usually used to ensure that the surface of aluminum is clean by soaking, spraying or ultrasonic cleaning.

For example, during the cleaning process, aluminum can be placed in an alkaline solution containing a surfactant, heated to the proper temperature and held for a certain period of time, and then rinsed clean with water.

2. Etching (optional)

For some aluminum materials that need special surface effects or to improve the adhesion of the oxide film, etching can be carried out. Etching is usually done by chemical etching to create microscopic rough structures on the surface of the aluminum.

For example, etching solution containing hydrofluoric acid and other ingredients can be used to treat the aluminum under certain temperature and time conditions, so that the surface shows uniform microscopic pits or raised structures, thereby increasing the bonding of the oxide film with the aluminum substrate.

Anodizing

1. Electrolyte preparation Commonly used electrolytes are sulfuric acid, chromic acid, oxalic acid and other acidic solutions. Different electrolytes will produce oxidized film with different characteristics.

For example, in the sulfuric acid anodizing process, the electrolyte generally adopts sulfuric acid solution with a concentration of 15% - 20%. Parameters such as temperature, concentration and agitation of the electrolyte will affect the growth and properties of the oxide film.

2. Anodizing process

Pre-treated aluminum as the anode, lead plate or stainless steel plate as the cathode, into the electrolyte, through the direct current. Under the action of the current, an oxidation reaction occurs on the surface of the aluminum material, generating a thin film of aluminum oxide.

During the oxidation process, parameters such as voltage, current density and oxidation time need to be controlled. Generally speaking, the higher the voltage, the faster the growth of the oxide film, but too high a voltage may lead to loose oxide film or breakdown; current density also affects the quality of the oxide film and the growth rate, usually need to be adjusted according to the composition of the aluminum, the area and the required thickness of the oxide film, etc.; oxidation time determines the thickness of the oxide film, the oxidation of the oxide film will be formed for a long time thicker oxide film, but it may make the oxide film hardness and corrosion resistance occur. The hardness and corrosion resistance of the oxide film will be changed.

Post-treatment

1. After anodizing, there will be some micropores on the surface of the oxide film, which need to be sealed to improve the protective performance of the oxide film. Sealing treatment usually adopts hydration sealing or steam sealing and other methods.

For example, hydration sealing is to put the anodized aluminum into boiling water, so that the micropores on the surface of the oxide film react with water to generate hydrated alumina, which closes the micropores; steam sealing is to use high temperature and high pressure steam to make the micropores on the surface of the oxide film be filled and closed.

2. Dyeing (optional)

If it is necessary to give color to aluminum, dyeing treatment can be carried out after the oxide film is formed. There are various dyeing methods, such as organic dye dyeing and inorganic pigment dyeing.

For example, organic dye dyeing is to put aluminum into the solution containing organic dyes, and through impregnation or electrolytic coloring and other methods, the dye molecules are adsorbed on the surface of the oxide film or infiltrated into the micropores, so as to achieve the purpose of dyeing; and the inorganic pigment dyeing is to attach the inorganic pigment particles on the surface of the oxide film through physical or chemical methods.
www.zgmetalceiling.com
3.Drying and aging treatment

After dyeing, the aluminum needs to be dried to remove the moisture on the surface. Then aging treatment is carried out to make the properties of the oxide film more stable. The aging treatment usually involves holding the material at a certain temperature for a certain period of time.

For example, the dyed aluminum is put into an oven and baked at a certain temperature for a certain period of time, so that the moisture in the oxide film evaporates, and at the same time promotes the bonding of the oxide film with the aluminum substrate to be stronger, and improves the performance of the oxide film in terms of hardness, corrosion resistance, and abrasion resistance.