What are the main ways of surface treatment for aluminum profiles?

The purpose of surface treatment of aluminum alloy extrusion materials is to solve or improve the three aspects of material corrosion resistance, decoration and functionality. The corrosion potential of aluminum is relatively negative, and the corrosion is more serious, especially when it is in contact with other metals, the problem of galvanic corrosion of aluminum is extremely prominent.

Therefore, the corrosion of the material is prevented by surface treatment methods such as anodized film and organic polymer coating to improve the corrosion resistance of the material. The decoration mainly starts from the appearance and improves the appearance quality of the material. Functionality refers to certain chemical or physical properties imparted to metal surfaces, such as increased hardness, improved wear resistance, electrical insulation, hydrophilicity, or imparted new functions (electromagnetic functions, optoelectronic functions, etc.) to the material.

In practical applications, it is rare to solve a certain aspect alone, and it is often necessary to consider it comprehensively. For the aluminum alloy extruded material for construction, due to its comprehensive properties such as corrosion resistance, weather resistance, wear resistance, good appearance decoration and long service life, subsequent surface treatment must be carried out to give the surface protective layer and decorative layer.

Aluminum surface treatment methods can be divided into: mechanical surface treatment, chemical surface treatment, electrochemical surface treatment, spraying polymer (physical treatment) and other physical methods.

• Mechanical Surface Treatment

Mechanical surface treatment is usually used as a pretreatment method, including sandblasting, shot peening, sweeping or polishing. Providing a uniform, smooth, smooth or textured, or even glossy surface for further surface preparation is generally not the final measure of surface preparation.

       Mechanical Surface Treatment

   Polishing for aluminum extrusion parts

Polishing process for extrusion aluminum cover 

• Chemical surface treatment

Generally, there are chemical pretreatment and chemical conversion surface treatment for aluminum. The former is also not the final surface treatment measures, such as degreasing, alkali cleaning, pickling, chemical polishing, etc., so that the metal surface can obtain a clean, no oxide film or bright surface state, so as to ensure and improve the subsequent surface treatment (such as anodizing) quality. And chemical conversion treatment, such as chromating, phosphorus. Chromating, chromium-free chemical conversion, etc., can be used as the bottom layer of the subsequent spray coating, or as a final surface treatment.

 Anodizing workshop

  Hanging electroplating for aluminum parts

• Electrochemical Surface Treatment

Anodized film is the most widely used method in electrochemical surface treatment, and it is an important method to solve the protection, decoration and function of aluminum. Electroplating is an electrochemical treatment process in which aluminum workpieces are used as cathodes. The plated metal is deposited on the surface of aluminum to form an electroplating layer by electrochemical reduction.

In recent years, micro-arc oxidation, also known as spark anodizing and micro-plasma oxidation, is the result of the combined action of electrochemical process and physical discharge process. The anodic oxide film is generally amorphous aluminum oxide, while the micro-arc oxide film contains a considerable amount of crystalline aluminum oxide, which is a high-temperature phase with high hardness, so the hardness of the micro-arc oxide film is particularly high, and the wear resistance is particularly high.

Galvanizing of acid containers in the plating workshop

    Aluminum plating process and workshop

• Spray treatment

Spray organic polymer coatings have developed rapidly in the finishing of architectural aluminum extrusions, almost on a par with anodizing.

At present, the organic polymers widely used in industry are polyacrylic resin (electrophoretic coating), polyester (powder coating), polyvinylidene fluoride (fluorocarbon coating) and so on.

Polyester powder is the main component of electrostatic powder spraying, which is generally sprayed on the chemical conversion coating of aluminum materials, and has been widely used in aluminum extrusion materials. Water-soluble coatings of polyacrylic resins have also been used as electrophoretic coatings for many years, and solvent-based acrylic coatings can also be sprayed with electrostatic liquids to form films. Fluorocarbon coatings are also sprayed with electrostatic liquids and are now considered to be the coatings with the best weather resistance.

However, solvent-based coatings inevitably cause air pollution due to toxic volatile organic compounds (VOCs), and there is a risk of fire. Europe has developed a new generation of high-durability powder with weather resistance close to fluorocarbon coatings, and it has been included in the European coating specification (Qualicoat), which is called "second-class powder". In addition, fluorocarbon powder has also come out, and foreign countries have entered the commodity market.

   Spray treatment process for aluminum extrusion parts

      Powder spraying and surface treatment

Products produced by anodizing color treatments, including electrocoating, currently account for about half of the architectural aluminum extrusion market. Electrophoretic paint is still dominated by transparent glossy paint, and matte paint and color paint have also been used.

In recent years, the production of powder-coated aluminum extrusions has developed rapidly, and currently accounts for more than 50% of the market in China. In the economically developed Yangtze River Delta region and the Pearl River Delta region in China, the market share of powder coating extrusion materials is estimated to be higher, with a trend of more than 60%.

After more than 20 years of development, the production process of aluminum building extrusion surface treatment in China has covered all the advanced technologies in the world, including anodizing, polyacrylic electrophoretic coating, polyester powder spraying, PVDF or polyacrylic liquid spraying, etc.

The technical equipment and technological level of production, product quality and variety have reached or approached the international advanced level.

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