Anodising Aluminium: Process, Techniques and Applications

Anodising Aluminium: Process, Techniques and Applications

Anodising aluminium is an electrochemical process that involves forming a layer of dialuminium trioxide [Al2O3 or aluminium(III) oxide] on this metal’s surface. Through anodising, aluminium gains a number of beneficial properties, such as increased corrosion resistance, hardness or aesthetic appearance.

What is aluminium anodising?

Anodic aluminium oxidation, also known as aluminium anodisation, is an electrochemical process that produces anodised aluminium.

The definition of anodic aluminium oxidation is based on the differences between anodising and other aluminium treatment methods. During anodising, aluminium is subjected to an electrolysis process in an acid bath, which leads to forming a dialuminium trioxide layer on its surface. Unlike other methods, such as painting or coating, anodising does not involve the applying any additional layers to the aluminium, but rather the transformation of a metal’s surface itself.

A layer of aluminium(III) oxide is porous and can be tinted in a variety of colours to create an attractive finish. In addition, this treatment makes the metal more resistant to abrasion and scratching.

Aluminium anodising process

The method of anodising aluminium involves an electrochemical process that consists of several steps:

  1. Surface preparation: Prior to anodising, the aluminium surface must be properly prepared. This includes degreasing, removing contaminants and possibly grinding or polishing to achieve a smooth texture.
  2. Preparing the electrolytic bath: Next, the products are submerged in an electrolytic bath, usually based on sulphuric or phosphoric acid. The acid concentration, temperature and anodising time affect the thickness and properties of an dialuminium trioxide layer formed.
  3. Connecting to a power source: Aluminium (Al) is connected as an anode and a conductive material, such as graphite or titanium, as a cathode. An electric current flows through the electrolytic bath, causing an electrochemical reaction on the aluminium’s surface.
  4. Electrochemical process: As a result of the electric current flow, a layer of dialuminium trioxide is formed on the surface. The thickness and porosity of this layer depend on the process parameters, such as current’s intensity, anodising time and the acid concentration in the electrolytic bath, the minimum is 5 µm.
  5. Colouring (optional): If we want to tint a surface, it can be submerged in a dye bath after anodising. The dye penetrates the porous structure of the aluminium(III) oxide layer, giving it the desired colour.
  6. Sealing: The final stage of anodising is surface sealing, which involves submerging the aluminium in a hot water or chemical bath. This process closes the pores in the dialuminium trioxide layer, increasing its resistance to corrosion and abrasion. An innovation in the chemical-thermal process treatment is the full or partial use of polymers. These result in the formation of a thermosetting furan resin, which completely seals the coating.

It is worth noting that the aluminium anodising process can be customised by changing the parameters in each step. By modifying the anodising time, acid concentration or current intensity, it is possible to achieve different properties of the anodic layer, such as thickness, hardness, sealing or colour.

The anodic layer and its properties

An anodic layer, also known as an anodic coating or dialuminium trioxide layer, is a thin but extremely durable and corrosion-resistant layer of dialuminium trioxide. These properties depend on the thickness and porosity of a layer, the thickness of which can be controlled by changing the parameters of the anodising process. Some of these properties are:

  • Corrosion resistance: The dialuminium trioxide layer protects the aluminium from atmospheric influences such as moisture and pollution, providing excellent corrosion resistance.
  • Hardness and durability: The coating is significantly harder than aluminium itself, which increases a surface’s durability and abrasion resistance.
  • Aesthetics: The anodised component can be tinted in any colour, allowing for an attractive appearance and individual character.
  • Adhesion: The porous structure of a dialuminium trioxide layer facilitates the grip of paints and adhesives, which is important when painting or gluing anodised aluminium components.
  • Thermal insulation: A dialuminium trioxide layer reduces the thermal conductivity of aluminium, which can be beneficial in certain applications, such as in the construction industry.

Use of anodised aluminium

Oxidised components are exploited because of their unique properties in many industrial sectors, as they allow for better quality products that meet the requirements of even the most demanding industries:

  • Construction: Building structures such as windows, doors, facades and balustrades.
  • Automation and robotics: Machine parts such as bodies, frames or connecting parts.
  • Electronics: Housings for electronic devices such as televisions, smartphones, tablets or computers.
  • Transport: Vehicle components such as bicycle frames, car structural components or ship and aircraft parts.
  • Advertising and design: Advertising components such as signboards, signs or advertising stands.

Advantages and benefits of anodising aluminium

By anodising aluminium, a material’s properties can be improved, which translates into better performance and aesthetics. Above all, the anodised surface becomes significantly more resistant to corrosion. The anodic layer, which is a dialuminium trioxide, protects the material from atmospheric agents such as moisture or airborne pollutants. As a result, anodised aluminium can be used in a variety of conditions, including those with high humidity or aggressive chemical environments.

Another advantage of anodising aluminium is the increased hardness of its surface. An anodic layer is much harder than the natural oxidation coating, which makes anodised aluminium more resistant to scratching, abrasion or impact. As a result, components made from anodised aluminium are more durable and perform better in a variety of applications, such as building structures, machine components or electronic equipment housings.

The process also improves the adhesion of paint coatings. An anodic layer has a porous structure, which allows the paint to adhere better to a surface. As a result, painting anodised aluminium produces more durable and aesthetic results than painting non-anodised aluminium.

The benefits of colour anodising lie in the possibility of achieving attractive visual effects. Through the use of organic or inorganic dyes, a variety of colours and shades can be achieved, which give anodised aluminium individuality. Colour anodising creates aesthetically pleasing and long-lasting finishes that work well in industries such as architecture, design and advertising.

Hard and coloured anodising

Hard anodising is a process that involves creating a harder and thicker layer of dialuminium trioxide on an aluminium’s surface than in the case of ordinary anodising. The hard anodising process is mainly used to increase abrasion and scratch resistance. In the case of hard colour aluminium anodising, in addition to increasing hardness and corrosion resistance, an important objective is to achieve an attractive appearance by dyeing the coating.

Among the methods of colouring aluminium, a distinction can be made between galvanic and colour anodising. Galvanic anodising involves the injection of a dye into the pores of an anodic layer during the anodising process to produce different colours and shades. The coloured anodising process is based on the use of organic or inorganic dyes, which are implanted into an anodic layer’s pores after it has been formed.

The popularity of colour anodising stems from the possibility to achieve attractive visual effects and to increase hardness and corrosion resistance. Consequently, colour anodising is often used in industries such as architecture, design, advertising or sports equipment manufacturing.

As far as the cost of colour anodising is concerned, it is usually higher than for plain anodising, due to additional process steps such as the dye insertion of the dye and colour solidification.

Types of aluminium surface treatment

Aluminium surface treatment is a process that aims to improve the functional and aesthetic properties of a metal. Among the various metal treatment techniques, in the case of aluminium, the most popular are anodised aluminium profiles, CNC machining and powder coating.

Anodised aluminium profiles are the result of the anodising process, which involves the formation of dialuminium trioxide coating on the surface of a metal. This coating forms a protective dialuminium trioxide layer that increases resistance to corrosion, abrasion and scratching. Anodised aluminium profiles are widely used in industry, construction, automotive and sports equipment manufacturing.

CNC (Computer Numerical Control) machining is a technique that allows aluminium alloys to be machined accurately and quickly using numerically controlled machines. Thanks to this method, it is possible to obtain complex shapes and dimensions with a high degree of accuracy. CNC machining is often used in the manufacture of machine components, equipment and in the aerospace industry.

Powder coating is another metal surface treatment technique, which involves applying powder paint to the surface of aluminium. The paint is then hardened at a high temperature to produce a durable and aesthetically pleasing coating. Powder coating is popular in industries such as construction, automotive and furniture manufacturing.

It is worth noting the importance of aluminium(III) oxide coatings in the context of surface treatment. Dialuminium trioxide layers not only increase corrosion resistance, but also improve the mechanical and thermal properties of aluminium. As a result, surface treatment of aluminium produces a material with better performance characteristics, which translates into wider application possibilities for the metal in various industries.

Innovations and the future of aluminium anodising

The safety of aluminium anodising influences its further development and implementation in industry. Innovations are being rolled out to make the process more efficient and also to improve its safety. One such innovation is the aluminium galvanisation, which allows acquiring even better protection against corrosion.

Recycling anodised aluminium is also an important aspect. Thanks to the possibility of recovering and reusing this material, anodised aluminium is becoming increasingly environmentally friendly.

Anodising innovations also include the introduction of new technologies that allow for better surface properties. An example of such innovation is aluminium sealing, which involves the use of special polymers to increase corrosion resistance and improve a surface’s durability.

In the future, aluminium anodising may also be used in conjunction with further treatment processes such as powder coating or varnishing. This could result in even better aesthetic and functional properties.


In this article, we have discussed the process, techniques and uses of anodising aluminium, which allow achieving unique surface properties of this material. We have described the basic processes, its steps and the resulting anodic layer. We have also discussed the application of anodised aluminium in various industries.

We encourage you to get acquainted with a wide range of aluminum anodizing in  CPP “PREMA” S.A., as well as to contact and cooperate in the creation of a high-quality wide range of electroplating products.