Aluminum clear anodizing is an electrochemical treatment that produces a transparent oxide film on the surface of aluminum. It can improve the corrosion resistance, surface hardness, and durability of aluminum while maintaining the original appearance of aluminum. The anodized surface still has a metallic texture and smoothness, which is very suitable for functional or decorative applications in various industries.
This article will introduce the clear anodizing process, key performance characteristics, appearance change factors, alloy compatibility, die casting application points, and common use areas. Read on to explore how to apply this process more effectively in actual manufacturing.
Clear Anodizing Steps
Surface Cleaning
Anodizing first requires thorough cleaning of the aluminum surface to remove oil, processing fluids, fingerprints, and oxides.
Usually, alkaline and acidic solutions are used in sequence to lay the foundation for the uniform growth of the subsequent oxide layer.
Etching or Brightening Treatment
Next, you can choose to etch (to form a uniform matte) or chemical brightening (to improve the surface gloss).
Etching helps to remove fine scratches and processing marks on the surface, while brightening is used to create a decorative gloss.
Anodizing Electrochemical Treatment (Mainly the Type II Sulfuric Acid Method)
Aluminum is immersed in sulfuric acid electrolyte, and oxygen is generated on its surface by electricity to form a controlled aluminum oxide layer.
Type II is the most commonly used anodizing method to achieve transparent effects.
The film thickness is generally between 0.0002″ and 0.001″, with excellent corrosion resistance and retaining the original color of the metal.
Sealed Oxide Layer
After oxidation, the surface needs to be sealed to close the porous oxide film, greatly improving the durability, discoloration, and corrosion of the parts.
Common methods include hot deionized water sealing, steam sealing, and nickel acetate sealing.
Physical and Chemical Properties of Clear Anodizing
Corrosion Resistance
The anodized layer forms a dense and stable oxide film on the surface of the aluminum, which effectively blocks the erosion of air, moisture, salt, and various chemical media.
Wear and Scratch Resistance
The surface hardness of the aluminum after oxidation treatment is significantly improved, and it has strong wear resistance and scratch resistance.
It is a surface strengthening method that combines strength and lightness.
Electrical Insulation
The anodized layer is a non-metallic insulator that effectively blocks the conduction of electric current.
Its uniform, stable, non-conductive surface prevents short circuits or signal interference.
UV Resistance
The anodized film has good light stability and can resist the decomposition and degradation effects caused by ultraviolet radiation.
Even after long-term exposure, it can still maintain a stable color.
Clear Anodizing Color Difference Factors
Not Really “Colorless”
Clear anodizing is not completely colorless. The color may appear silver, gray, champagne, or bronze, depending on the alloy and process.
Alloy Composition
High-purity aluminum, such as 1050 or 6063, has a brighter surface and more uniform color, while alloys containing copper or silicon, such as 2024 or A380, tend to darken or have obvious color differences.
Film Thickness
The thicker the film, the easier it is to absorb light and present a darker or grayer tone. Thin films are more transparent and reflective.
Sealing Method
Hot water sealing is prone to produce a slight rainbow luster, while cold sealing or nickel acetate sealing is more transparent and has a matte surface.
Suitable Aluminum Alloys for Clear Anodizing
Recommended Alloys
Low copper and low silicon alloys such as 6061, 6063, 1050, and 1100. These alloys have low impurity content and good anodizing reactivity.
After oxidation, they can form a uniform, stable, and firm transparent oxide film.
Unrecommended Alloys
High copper or high zinc alloys, such as 2024 and 7075, are prone to color differences after clear anodizing, dark surface, poor adhesion of the oxide layer, and low corrosion resistance, which is not conducive to obtaining an ideal appearance and stable performance.
Clear Anodizing for Aluminum Die Castings
Is It Possible?
Yes, but extra attention is required. Die-cast aluminum alloys have a high silicon content, which can easily affect the quality of the oxide layer. Alloy selection and the pre-treatment process are crucial.
Common Problems
High silicon content will cause black and gray after oxidation, and porous surfaces are prone to spots, unevenness, poor adhesion, and other problems, especially affecting the appearance of parts.
Recommended Practical Solutions:
- Prefer low-silicon alloys such as AlSi9Cu3 or A356
- Additional polishing or sealing before oxidation to reduce porosity
- Test a small batch of samples first to confirm the color and adhesion effect
- Avoid deep cavities or complex structures to reduce blind spots in anodizing
Applicable Fields
Clear anodized aluminum die casting parts are often used in electronic product housings, lighting fixtures, outdoor equipment housings, automotive decorative parts, etc., with both structural and visual requirements.
Not Recommended Fields
If there are extremely high requirements for appearance consistency or high gloss, clear anodizing may not be the best choice.
It is recommended to consider alternative processes such as powder spraying or painting.
Typical Applications of Clear Anodizing
Architecture
Such as window frames, curtain walls, railings, and door panels, with strong weather resistance and a durable appearance.
Consumer Electronics
The shells of products such as laptops, mobile phones, and headphones are often treated with clear anodizing to improve texture and scratch resistance, and are also convenient for laser engraving of brand logos.
Automotive
It is used in interior trims, control panels, lightweight brackets, and other parts, taking into account lightweight, appearance, and anti-corrosion requirements.
Medical
The surface is easy to clean and disinfection-resistant, and is often used in scenes such as shells, instrument panels, and surgical trays.
Industrial Equipment
Control panels, radiators, equipment housings, etc., clear anodizing enhances their wear resistance and environmental adaptability, and is suitable for harsh environments such as large temperature differences and high humidity.
Comparison Between Clear Anodizing and Other Surface Treatments
Raw Aluminum Surface (Mill Finish)
Without any protective layer, the surface is dull and easily oxidized, and cannot provide corrosion resistance or mechanical protection.
In contrast, clear anodizing provides a uniform protective layer, improving durability and appearance stability.
Satin Anodizing
Brushing is added before anodizing, and the surface is softer and matte. Compared with standard clear anodizing, satin texture is more delicate but less reflective.
Hard Anodizing
The film is thicker and harder, suitable for heavy-duty conditions. The clear anodized film is thinner and more natural in appearance, suitable for treatments that require appearance and precision.
Powder Coating
The coating covers the surface with rich colors, but is prone to aging, peeling, or cracking over time.
Clear anodizing is combined with the aluminum body, making it less likely to fall off, and it has stronger scratch resistance.
Spray Painting
The adhesion of the paint is affected by the substrate and process, the thickness of the paint layer is difficult to control, and the corrosion resistance depends on the quality of the surface treatment.
The clear anodized film is uniform and stable, and the overall performance is more controllable.
Electrophoretic Coating
Provides good corrosion resistance and decorative properties, but has high requirements for substrate cleanliness and relatively fixed color control.
Clear anodizing has a natural metal texture and higher visual consistency.
Conclusion
Clear anodizing improves the corrosion resistance, surface strength, and appearance of aluminum and meets both functional and decorative needs.
When properly applied, it works just as reliably on die castings.
As a professional aluminum die casting manufacturer, CEX Casting provides one-stop solutions from mold design to surface treatment, ensuring stable results and outstanding quality.
Contact us today to learn how we can help you improve your next aluminum die casting project.