What is Alodine? Alodine definition, process, benefits, influencing factors, considerations, applications

What is Alodine? Alodine definition, process, benefits, influencing factors, considerations, applications

Ⅰ Introduction to Anodizing

Chromic acid anodizing, also known as chromate anodizing, is a metal surface treatment technology, widely used in the surface treatment of aluminum and aluminum alloys. The process is performed by using chromic acid (CrO;) And other additives in the electrolyte, a voltage is applied to the aluminum to form a dense oxide film on its surface. This layer of oxide film not only has good corrosion resistance, wear resistance and decorative, but also can enhance the adhesion of aluminum and coating, improve the overall performance and service life of the product. Because of its unique properties, chromic acid anodizing has been widely used in aerospace vehicle manufacturing, architectural decoration, electronic communication and other fields.

Ⅱ Anodizing process

1.Pretreatment

Cleaning: Remove grease, dust and other contaminants from the surface of the workpiece. This step usually involves degreasing and washing.

Chemical degreasing: Use an alkaline solution to remove oil.

Pickling: Removal of oxide and minor corrosion, sometimes using mechanical methods such as sandblasting to remove surface defects.

Neutralization: If pickling is performed, neutralization is required to remove residual acid.

Activation treatment: The use of appropriate activators to promote the formation of oxide film.

2.Anodizing

Anodizing tank preparation: Prepare an electrolyte containing chromic acid or its salts, commonly a mixture of chromic anhydride (CrO3) and sulfuric acid (H2SO4).

Preheating: preheating the workpiece to a certain temperature helps to form a uniform oxide film.

Power on: the workpiece is placed in the electrolyte as an anode and a direct current is applied. At this point, the aluminum surface begins to form an oxide film.

Control parameters: Adjust parameters such as current density, electrolyte temperature and processing time according to the thickness and quality of the desired film.

3.Post-processing

Sealing treatment: In order to improve the corrosion resistance of the film layer and close the pores, hot water sealing or boiling water sealing is usually carried out, and sometimes substances such as water glass are added to further improve the sealing effect.

Drying: Dry the treated workpiece to remove surface moisture.

4.Test

Check the appearance of the processed workpiece to ensure that there are no defects, such as cracks, spots, etc.

It may also include film thickness testing, adhesion testing, etc.

5.Packing into storage

Proper packaging of qualified workpieces to prevent damage during storage and transportation.

Ⅲ Anodizing advantages

1. Excellent corrosion resistance

The chromic acid anodizing oxide film is very dense, which can effectively isolate the contact between the metal and the corrosive media in the environment (such as oxygen, water, salt spray, etc.), thus significantly improving the corrosion resistance of aluminum. This is particularly important for components that operate in harsh environmental conditions.

2. Good wear resistance

The chromic acid anodized film is not only corrosion resistant, but also has high hardness and wear resistance, which can effectively resist mechanical wear and scratches and extend the service life of the product.

3. Excellent decoration

By adjusting the anodizing process parameters, the color depth and uniformity of the film layer can be controlled, so that the aluminum surface presents a rich color and luster, and has a good decorative effect. This feature is especially popular in architectural decoration, household goods and other fields.

4. Enhance the adhesion of the coating

Chromic acid anodized film can improve the microstructure of aluminum surface, improve the adhesion with organic coatings (such as paint, varnish, etc.), ensure that the coating is not easy to fall off, and improve the overall quality and beauty of the product.

5. Process flexibility

Chromic acid anodizing process is relatively mature, the parameter adjustment range is wide, can be customized according to the specific needs of different thickness, color and performance of oxide film, to meet the requirements of different application fields.

6. Good insulation

The chromic acid anodized film also has certain electrical insulation properties, which is advantageous for application scenarios requiring electrical isolation.

7. Low cost and high efficiency

Compared with other surface treatment methods, the chromic acid anodizing process is mature and stable, the production cost is relatively low, and the added value and market competitiveness of the product can be significantly improved.

Ⅳ Influencing factor

1. Electrolyte composition: chromic acid concentration, additive type and content directly affect the formation speed and quality of the film layer.

2. Process parameters: the setting of voltage, current density, temperature, time and other parameters has a significant impact on film thickness, color, density and so on.

3. Base material properties: the purity of aluminum, alloy composition, surface state, etc., will also affect the anodizing effect.

Ⅴ Care and maintenance

1. Electrolyte management: Regular detection of electrolyte composition, timely adjustment and supplement to ensure stable electrolyte performance.

2. Equipment maintenance: Check the working status of the power supply, cooling system, mixing device and other equipment, and regularly clean and maintain.

3. Safety protection: chromic acid and other chemicals are harmful to human body. Wear protective equipment when operating and ensure that the working environment is well ventilated.

Ⅵ Matters needing attention

1. Operation safety: strictly comply with chemical operation specifications to prevent splashing into eyes or skin contact.

2. Environmental protection: The waste liquid after treatment can be discharged after environmental protection treatment to reduce the impact on the environment.

3. Quality control: Regularly test the quality of the anodized film layer to ensure that the product meets the standard requirements.

Ⅶ Anodizing application

Aerospace parts: Many parts of an aircraft, such as wings, fuselage structures, interior trim, etc

Military equipment: Tanks, armored vehicles, firearms and other military hardware are often anodized with chromic acid to enhance their protection and ensure normal operation in a variety of harsh environments.

Electronic devices: smart phones, laptops and other consumer electronic products shell, not only can beautify the appearance of the product, but also enhance its scratch resistance and corrosion resistance.

Building hardware: Door and window handles, hinges, slides and other building hardware through chromic acid anodization, can maintain a good appearance and function in the case of long-term exposure to the outdoor environment.

Medical equipment: Medical supplies such as surgical instruments and diagnostic equipment, after anodizing, are easier to clean and disinfect, and can be maintained in good condition under frequent use.

Transportation: The interior decoration parts and external parts of vehicles such as cars, trains and buses can effectively resist wear and environmental erosion in daily use through chromic acid anodizing.

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