Anodising is an electrolytic passivation process designed to increase the thickness of the natural oxide layer on the surface of metal parts.  Anodising forms this dense oxide layer on aluminium and its alloys via electrolytic conversion. This oxide layer successfully resists abrasion and so protects the underlying metal.  The thicker the oxide layer, the more protection provided.  

The process is called anodizing because the metal component to be treated takes the role of the anode electrode in an electrical circuit.

Some benefits of anodising are:

  • Improved wear resistance and hardness
  • Scratch resistant
  • Excellent metal protection and corrosion resistance
  • Better adhesion for paint primers and glues than bare metal
  • Cost effective

Hard and Natural Anodising

At Anodisers Runcorn we are able to perform both natural and hard anodising. Generally hard coatings are required between 25 microns and 50 microns, although it is possible to achieve thicker deposits.  A hard anodised finish has a micron hardness of approximately 1100 HV which provides superb corrosion and temperature resistance, and excellent electrical insulation.

Hard anodising is possible in various colours, but the final finish tends to be darker than natural anodising.

Anodised Fork Yoke

Decorative and Colourful

Anodising is done primarily to protect against metal corrosion, but an anodised metal finish also has a pleasing aesthetic appearance.  The naturally anodised metal is silver or light grey, depending on the aluminium alloy and its surface finish.  A wide variety of other colours can be achieved using dyes.  The brightness of the finish achieved is largely due to the purity of the aluminium, but it can be enhanced by chemical, mechanical or electro-chemical methods.

Perfect for Architectural Applications

An anodised aluminium finish is often needed for external building applications, where a combination of aesthetics, mechanical performance and corrosion resistance are important.

Issues to Consider When Anodising

Aluminium Alloys Suitable for Anodising

  • 1000 Series-Say 1080A, 1200A, 1050 - ideal for anodising
  • 2000 Series-Say 2014A, 2024 - a satisfactory anodised layer can be produced
  • 3000 Series-Say 3103, 3105 - ideal for anodising
  • 4000 Series-Say 4043A,4047A - a satisfactory anodised layer can be produced
  • 5000 Series-Say 5005, 5056, 5083, 5251, 5454 - ideal for anodising
  • 6000 Series-Say 6061, 6063, 6082, 6262, 6463 - ideal for anodising
  • 7000 Series-Say 7020, 7075 - ideal for anodising

Suitable Casting Alloys

Generally, LM25 and LM5 and some other alloys are suitable.  Please contact us for recommendations.


Any non-aluminium components will erode during the anodising process and therefore must be removed in advance.

Surface Finish

Any existing flaws on the part’s surface will grow more apparent after anodising as the process maximises the surface’s appearance.  The surface finish before anodising needs to be of a higher standard than that expected of the finished product.


Selective Anodising

For areas which do not require an anodised finish, simply masking them will exclude them from the process.


Attention needs to be given to the jigging location, as this area won’t be anodised.  An electrical contact must be made with each item for the anodising process to be successful.