What is the secret of surface treatment to extend the service life of aluminum by more than 2 times?

The service life of aluminum is extended by more than 2 times, and its surface treatment often uses a combination of processes and technologies, here are some key tips:

Cleaning pre-treatment

Thorough degreasing: Aluminum will be contaminated with various oil stains during processing, transportation and storage, such as lubricating oil, anti-rust oil, etc. If it is not completely removed, it will affect the adhesion of the subsequent coating. It can be cleaned with organic solvents (such as trichloroethylene, acetone, etc.), lye cleaning (such as lye formulations composed of sodium hydroxide, sodium carbonate, etc.) or surfactant cleaning. For example, in the production of some precision aluminum parts, trichloroethylene will be used for ultrasonic cleaning first, which can effectively remove oil stains in the subtle crevices and lay a good foundation for subsequent treatment.

Descaling and rust removal: If there is a naturally occurring oxide film, dirt or slight rust on the surface of the aluminum, it needs to be treated accordingly. For general oxide films, chemical polishing slurries (such as formulas composed of phosphoric acid, sulfuric acid, chromium anhydride, etc.) can be used to treat the surface to make its surface smooth and bright; For more serious rusts, mechanical grinding (such as sandpaper sanding, sandblasting) or chemical rust removal (such as using pickling solutions such as hydrochloric acid and nitric acid, but attention should be paid to controlling the concentration and treatment time to avoid excessive corrosion). For example, before installation, aluminum profiles for construction are usually sandblasted to obtain a uniform surface roughness and enhance the adhesion of subsequent coatings.

Activation: Activation of the surface of the aluminium can increase its activity and promote the bonding of the coating to the substrate prior to coating or other surface treatments. Common methods include activation before anodic oxidation (such as short-term electrolysis in dilute sulfuric acid solution), chemical activation (treatment with solutions containing fluoride, titanium salts, etc.). For example, chemical activation of aluminium prior to powder coating allows the powder coating to adhere better to the surface of the aluminium and form a strong coating.

Coating treatment

Anodizing: This is a widely used and effective surface treatment technology for aluminum. Through electrolysis, a dense alumina film layer is formed on the surface of the aluminum. This coating has the advantages of high hardness, good wear resistance and strong corrosion resistance, which can significantly improve the service life of aluminum. For example, in the field of architectural decoration, aluminum alloy doors and windows can effectively resist acid and alkali erosion in the atmosphere and ultraviolet radiation after anodizing, and prolong their service life. According to different application requirements, different anodic oxidation process parameters can be selected, such as sulfuric acid anodizing, chromic acid anodizing, oxalic acid anodizing, etc., among which sulfuric acid anodizing is the most commonly used, which can form an oxide film with a thickness of about 5 - 20 μm.

Powder coating: The powder coating is evenly applied to the surface of the aluminum by electrostatic spraying, and then cured at high temperature to form a strong coating. There are many types of powder coatings, including polyester powder, epoxy powder, acrylic powder, etc., which can be selected according to different use environments and performance requirements. Powder coating has good weather resistance, corrosion resistance and decoration, and is widely used in architectural aluminum profiles, home appliance shells and other fields. For example, aluminum billboards used outdoors can maintain their aesthetics and performance for a long time in harsh climatic conditions after being powder-coated.

Fluorocarbon spraying: It is a high-end surface treatment technology, and the fluorocarbon coating used has excellent weather resistance, corrosion resistance, chemical resistance and self-cleaning. Fluorocarbon-coated aluminum can be used outdoors for more than 20 years without obvious fading, chalking and corrosion, and is often used in high-end building curtain walls, bridge guardrails and other occasions with high durability requirements. The coating thickness is generally about 30-40μm, and the quality and performance of the coating are guaranteed through the process of spraying and baking.

Electrophoretic coating: Using the principle of electrochemistry, the charged paint particles are deposited on the surface of the aluminum under the action of the electric field to form a coating. The electrophoretic coating is uniform, flat and smooth, with good corrosion resistance and decoration, and has good environmental performance. The common ones are anodic electrophoresis and cathode electrophoresis, and cathode electrophoresis coating is more widely used, often used in the surface treatment of auto parts, hardware accessories, etc.

Sealing treatment

Hot water sealing: The anodized aluminum is immersed in hot water (generally 90 - 100 °C) to make the electrolyte in the pores of the oxide film undergo a hydrolysis reaction to generate aluminum hydroxide and other substances to fill the pores to achieve the purpose of sealing the pores. The cost of hot water sealing is low and the operation is simple, but the requirements for water quality are high, otherwise it is easy to produce poor sealing and corrosion problems.

Steam sealing: It is similar to the principle of hot water sealing, but using steam as the sealing medium, the sealing speed is fast, the effect is good, and it is suitable for large-scale continuous production. The oxide film after vapor sealing has better corrosion resistance and wear resistance.

Nickel salt sealing: The oxide film is sealed in a solution containing nickel salts, and nickel ions are hydrolyzed and deposited in the pores to form a dense sealing layer. The sealing effect of nickel salt sealing is good and the corrosion resistance is strong, especially suitable for occasions with high requirements for corrosion resistance, but the cost is relatively high, and it is necessary to pay attention to the environmental pollution of nickel ions.

Nickel-free sealing: With the improvement of environmental protection requirements, nickel-free sealing technology has received more and more attention and development. Common nickel-free sealing methods include zirconium salt sealing, titanium salt sealing, etc., which use nickel-free chemical reagents for sealing treatment, which can not only achieve good sealing effect, but also meet environmental protection requirements.