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Functional and decorative finishing of aluminum components as anode in special electrolytes

Aluminum-based alloys are becoming ever more popular as industrial construction materials. The low weight reduces inertia, which in turn saves energy. The disadvantage: aluminum alloys are prone to wear and corrosion.

Technical anodizing of metals such as aluminum or titanium is a functional coating solution delivering both protective and decorative results.

What is anodizing?

Technical anodizing is a classic anodizing process performed in acidic electrolyte at a temperature slightly below ambient. An external power source is used, while the workpiece is used as anode. Anodized metal finishes provide many benefits, including a higher breaking strength, and an increased corrosion and wear protection. This electrochemical process is most frequently used to create anodized aluminum sheets and components, but we also provide anodized titanium finishes.

The surface of the aluminum base material is transformed into aluminum oxide. One third of the coating created with technical anodizing grows out of the metal, whereas two thirds grow into it. That is why the bond between the coating and the base material is extraordinarily strong. What is more, coatings created with technical anodizing can meet different decorative requirements. To this end, preliminary treatments such as pickling, grinding, sandblasting or polishing are performed.

Anodization also makes dyeing possible: anodized aluminum and titanium can come in various colors, to achieve the functional or decorative effect desired. At Aalberts surface treatment, we offer, for example, both natural and black anodized aluminum finishes, but other colors are also possible using pigments.

Technical aluminum anodizing creates durable coatings in media which are neither too acidic nor too alkaline. Depending on the coating thickness and sealing, the coating is even able to temporarily withstand acidic or slightly alkaline attacks. The hardness of coatings created with technical anodizing is influenced by the material composition, especially by the alloy components. Coatings created with technical anodizing increase the wear resistance of aluminum to a significant extent.

Be it wrought alloys, cast alloys or die-cast alloys, almost all technically interesting aluminum alloys can be finished with technical anodizing. However, the type of alloy has a major influence on the color of the product to be anodized. It is also possible to deliberately create black oxide coatings. In order for a base material to be recyclable, the finish too needs to fulfill the conditions for recyclability. Anodic coatings, such as those created with technical anodizing, meet this requirement - another advantage offered by this type of protective coating.

  • Ideal protection against wear
  • High corrosion protection
  • Massive breaking strength
  • Excellent tribological properties
  • Protection against cold welding
  • Vibration resistance
  • Extreme temperature stability

Using different electrolytes and process parameters, we allow conductive oxide layers to “grow out” of the material. This anodizing process creates excellent structures and thus long-lasting surface finishes.

Fields of use of anodic oxidation

Aluminum sheets and components finished with technical anodizing offer good corrosion and wear protection in almost all industries: construction industry, chemical industry, computer industry, electrical engineering, vehicle construction, household devices and goods, lighting industry, aerospace industry, mechanical engineering, medical technology, furniture and fittings industry, optics/precision engineering, sports and camping as well as the textile industry. Technical anodizing is also used to create a protective base layer which is applied prior to varnishing in order to protect components against corrosion.

Thanks to the tried and tested surface finishes created by Aalberts surface treatment, it is easily possible to coat components with decorative colors and simultaneously protect them against corrosion. Components made of aluminum alloy are anodized in an electrolyte with color additives, whereas components made of titanium or titanium alloys are anodized in a special acidic electrolyte. The coating process creates a very thin, tenacious, colorless titanium oxide layer. It appears colored through interference (overlapping of light waves) and stands out with UV resistance. Using this method, we can create black, titan gray, blue, red, gold and green finishes. By varying the coating thickness, however, certain base materials may be finished in further colors. Apart from their color, titanium oxide coatings offer excellent electric isolation and biocompatibility.

Be it wrought alloys, cast alloys or die-cast alloys, almost all technically interesting aluminum alloys can be finished with color anodizing.

When it comes to titanium materials, however, things become a bit more complicated. The alloy most suitable for color anodizing is TiA16V4. The result: strong, reproducible colors of good quality.

Ti2 may also be coated in a wide range of colors. Unlike with TiAl6V4, the colors shift toward blue and appear somewhat subdued.

Reproducible color anodizing of pure titanium is limited to blue and yellowish finishes. This material is not suitable for decorative purposes.

Color-anodized aluminum components can be used wherever decorative colors and protection against corrosion and wear are paramount. These requirements are found in the area of architecture as well as in the electrical engineering, image and video technology, household devices, hunting weapons, sports articles or bicycle industries. Of course, the process is also used to create coatings in the automotive industry or surface finishes in mechanical engineering.

Color-anodized titanium materials are also used in medical technology: Titanium-based implants, which remain inside the body for a limited period of time to promote the healing of bone fractures, for instance, are finished with color anodizing in order to allow surgeons to quickly identify the components concerned. The coated implants behave neutrally in the body. As they adhere neither to the bones nor to the tissue, they can be easily removed upon completion of the healing process.

Due to their biocompatibility and decorative look, colored titanium oxide coatings may also be used in the optics and jewelry industries, e.g. for watches or jewelry goods. The bicycle industry prefers titanium materials because they are light and yet extremely resilient. Using color anodizing processes, it is also possible to meet the design requirements of customers who are interested in purchasing wheel nuts, for instance.

  • Does anodizing also work with other metals?

    So-called refractory metals - which include, amongst others, titanium, magnesium, zinc and vanadium - are suitable for anodizing. When it comes to the finishing of magnesium and titanium, Aalberts surface treatment offers two plasma-chemical processes: MAGOXID-COAT® (for magnesium) and KEPLA-COAT® (for titanium and aluminum).

  • What anodizing colors are available for aluminum?

    Anodic coatings have an inherent color which depends on the aluminum alloy and the process parameters used, such as the electrolyte composition or temperature. Higher electrolyte temperatures result in brighter coatings, whereas greater coating thicknesses create darker layers, making it possible to create black anodized aluminum coatings. Anodic coatings have pores which form as a result of the anodizing process. It is possible to dye the coatings by introducing pigments into these pores.

  • Is white anodizing possible?

    White coatings are created using the KEPLA-COAT® white (for aluminum and titanium) and MAGOXID-COAT® white (for magnesium) processes. Here, too, the coating color depends on the alloy.

  • Are there any dimensional limits and weight restrictions as regards the component to be anodized?

    The maximum dimensions are 7700x1000x1800 mm³, whereas the weight is restricted to 5000 kg. However, these restrictions always depend on the coating plant. Why not use our dimension tool to find out whether your dimensions are appropriate?

  • What is so special about these layers?

    These coatings are so-called conversion coatings. Parts of the base material become fully integrated with the coating, which results in an extremely high bonding strength between the anodic layers.

Product enquiry

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