Types of Coating on Aluminium
Aluminum and its alloys naturally develop an oxide film with some corrosion resistance. However, in building, industrial, transportation, electronics, and household applications, additional coating and surface treatments are often applied to further improve appearance, corrosion resistance, wear resistance, and functional properties. The following are the main processes and their characteristics.
Anodizing (Hardcoat Anodizing)
Anodizing is an electrochemical process that forms a dense, protective aluminum oxide (Al₂O₃) layer on the surface of aluminum in an acidic solution. The typical coating thickness is 10–15 μm; however, thermal oxidation can achieve up to 25 μm, and hard anodizing processes can produce coatings in the range of 30–100 μm.
Anodized aluminum offers excellent corrosion and wear resistance, a strong metallic appearance, and no risk of peeling. The porous layer can be colored with dyes.
Anodized coatings are commonly used in architectural profiles, electronic device housings, and decorative hardware.
Powder Coating
Powder coating is a process in which thermosetting powder is electrostatically sprayed onto the surface of aluminum. The coated part is then heated to cure the powder, forming a continuous organic coating with a typical thickness of 60–120 μm.
Powder coatings offer a wide variety of colors and textures, such as matte, metallic silver, and fine texture finishes. High weather-resistant powders are available for outdoor durability. The coating provides good corrosion and impact resistance.
Powder coating is widely used for architectural doors and windows, railings, curtain wall panels, and other aluminum products requiring decorative and protective finishes.
Liquid PVDF Coating (Fluorocarbon Coating)
Liquid PVDF coating, also known as fluorocarbon coating, is a multi-layer solvent-based system containing polyvinylidene fluoride (PVDF) resin. The process typically involves multiple coats (primer, intermediate, and topcoat), each with a thickness of 25–35 μm, resulting in a total film thickness of 40–60 μm.
PVDF coatings provide outstanding weather resistance and UV stability, maintaining color and gloss for 20 to 30 years. They offer excellent chemical resistance and are highly resistant to chalking and degradation. However, the process is relatively costly compared to other coating methods.
Liquid PVDF coatings are primarily used for high-standard architectural curtain wall panels and other exterior applications requiring long-term durability and premium appearance.
Electrophoretic Coating (E-coating)
Electrophoretic coating, or E-coat, is a process in which a water-based resin is deposited onto the aluminum surface under an applied electric field (either cathodic or anodic types). Prior to coating, the aluminum is typically anodized to create a porous surface structure, improving paint adhesion.
E-coat produces a uniform and thin film with excellent coverage, even on complex shapes. Its corrosion resistance surpasses that of conventional anodized coloring, and the finish is smooth with a semi-transparent metallic appearance. However, the color range is relatively limited compared to other coating systems.
Electrophoretic coating is widely used for window and door profiles where a refined texture is desired, as well as for bathroom hardware and various decorative components.
Coil Coating (Roll Coating)
Coil coating, also known as roll coating, is a continuous process in which aluminum coils are coated using rollers and then baked to cure the applied paint. A variety of coatings can be used in this process, including polyester (PE), silicon-modified polyester (SMP), polyurethane (PU), FEVE, and PVDF.
This method provides stable and consistent quality, high production efficiency, and precise control over coating thickness. The process is well-suited for mass production and accommodates a range of paint systems to meet different performance requirements.
Coil coating is widely used for roofing panels, wall cladding, aluminum honeycomb panel facings, and appliance panels, where uniform finishes and high throughput are essential.
Heat Transfer Printing for Wood and Stone Grain
Heat transfer printing is a technique used to apply wood grain or stone patterns onto aluminum surfaces. The process begins with anodizing the aluminum to create a porous, receptive layer. A patterned transfer film is positioned on the aluminum, and heat and pressure are applied, allowing the pattern to penetrate and adhere to the surface.
This method delivers high decorative value by closely simulating the appearance of real wood or stone. The cost is significantly lower than using natural materials, and the weather resistance exceeds that of traditional wood, making it suitable for long-term use in various environments.
Heat transfer printing is commonly used for interior and exterior decorative elements, such as wall panels, doors, window profiles, and architectural trims.
