What is Anodising? – Process and Uses

What is Anodising?

Anodising is an electrochemical surface treatment used to promote and increase the formation of an anodic oxide coating on a base material. For example, aluminium and its alloys are most commonly anodised to produce an aluminium oxide coating.

The anodising process involves submerging aluminium or an aluminium alloy into an electrolytic solution, such as sulphuric acid, alongside a cathode. When the aluminium alloy is fully submerged, an electrical current is passed through the aluminium, creating a cell. In this process, the aluminium takes on the role of the anode, therefore readily oxidising within the electrolytic solution. Anodising causes the aluminium to oxidise, therefore forming a thick layer of aluminium oxide (oxide film). This is opposed to the layer that would have naturally occurred which would be thinner and less effective.

What does Anodising Aluminium mean?

Anodising aluminium is a process used to produce a thick oxide film (anodic layer) for the aluminium/its alloys. This process is used to improve the corrosion and erosion resistance of the surface of the metal, whilst also decreasing its thermal and electrical conductivity.

Why is Anodising used?

The process of anodising is used to produce a thicker, more efficient aluminium oxide film (anodic layer) within a controlled process/environment as opposed to the layer of aluminium oxide that would occur naturally. The benefits of anodising a material such as aluminium include the increased corrosion and wear resistance of the oxide film (anodic layer) which is produced. This process forms a coloured layer on top of the material.

What Materials can be Anodised?

Aluminium and its alloys are the most common materials to be anodised, however, other materials that can undergo anodising include, steel, hafnium, zinc, titanium and magnesium.

Industry Applications

Anodising is used and applied within multiple different industries. TWI Ltd has experience in the process, including:

• TWI has experience with the colour matching properties/benefit of anodising.
• TWI has knowledge and experience with the recommended methods of surface preparation of aluminium alloys.
• TWI carried out an Industrial Member report looking into the environmental testing of polymer coated material joints. It looked at the surface pre-treatment of aluminium using anodising.
• TWI have produced published papers looking into the joining of polyethersulphone to aluminium by ultrasonic welding. This looked at reducing joints with poor mechanical integrity using anodising.
• TWI’s Surface Engineering and Coating Laboratory supports the development and application of new coatings that use anodising to create resistance to corrosion.