Aluminium anodising is an electrochemical process that enhances the natural oxide layer on the surface of aluminium. This process makes the aluminium more resistant to corrosion, increases its durability and allows it to be coloured for aesthetic purposes. Anodised aluminium is widely used in applications such as architectural structures, automotive parts, electronics and consumer goods.

How anodising works

The anodising process involves the following steps

1. Preparation and cleaning:
– The aluminium part is first cleaned to remove any surface contaminants, oils or oxides. This ensures that the anodising process can produce a uniform coating.
– Depending on the finish required, the surface may also be chemically or mechanically polished prior to anodising.

2. Electrolytic oxidation:
– The aluminium part is immersed in an acidic electrolyte bath, usually sulphuric acid.
– The aluminium acts as the anode (positive electrode) in an electrochemical cell, while a cathode (negative electrode) is placed in the solution.
– When a direct current (DC) is applied, oxygen ions from the electrolyte react with the aluminium surface to form a thick, porous layer of aluminium oxide (Al₂O₃).

3. Formation of the oxide layer:
– The thickness of the oxide layer can vary depending on the voltage and time of the anodising process. Higher voltages and longer times result in thicker layers.
– The aluminium oxide layer is much harder and more corrosion resistant than raw aluminium.
– This oxide layer is porous, making it suitable for colouring.

4. Colouring (optional):
– If a coloured finish is desired, the porous oxide layer can be dyed with various pigments.
– The pigments penetrate the pores of the oxide layer, resulting in a coloured surface that is resistant to fading.

5. Sealing:
– After colouring (if applicable), anodised aluminium is often sealed to close the pores of the oxide layer.
– This is done by immersing the anodised part in boiling deionised water or other sealing solutions, which hydrates the oxide and closes the pores.
– Sealing increases the corrosion resistance of the aluminium and locks in the colour, making it more durable.

Benefits of anodising aluminium

Corrosion resistance: The anodised layer acts as a protective barrier, preventing the aluminium from reacting with moisture and other environmental factors.

Durability: The anodised layer is hard and wear resistant, making it suitable for applications that require a tough surface.

Aesthetic appeal: Anodised aluminium can be dyed in a wide range of colours, providing flexibility for design and branding.

-Non-toxic and environmentally friendly: The anodising process doesn’t produce any hazardous by-products, making it more environmentally friendly than other coating methods such as painting or electroplating.

Overall, anodising not only extends the life of aluminium components, but also enhances their visual and functional properties, making it a popular choice in many industries.