Hard Anodising Basics

Standard anodic films are generally limited to a maximum of 30 microns in thickness. But if the temperature of the acid bath is lowered to near freezing point and the voltage is increased, anodic thicknesses of up to 100 microns can be achieved. These thicker anodic coatings have exceptional hardness characteristics and are very suitable for tougher engineering applications. This variation to the anodising process is commonly know as ‘hard’ anodising or ‘hard coat’ anodising.

The performance of the coating is dependant on the type of aluminium alloy used. The alloying ingredients will also influence the final colour of the product. Generally, hard anodic films have a dark grey or yellowish-brown tint.

The process is unlike other finishing methods, where the surface is coated with an organic or inorganic deposit. In contrast, anodising is a conversion of the base material to form a protective oxide coating.

Almost all anodising processing requires the components to be racked. Although we have many standard racks in stock, it may be necessary to construct special racks for some jobs, which may incur extra charges.

Before the anodising process commences, the part must be chemically cleaned. This most often involves a mixture of alkaline cleaners to remove oils and surface contamination. This is generally followed by an acid or caustic etching process.

Due to the density of the coating formed in the hard anodising process, it is always difficult to apply dyes to the resulting finish. The standard anodising process accepts dyes much more readily than hard anodising.

You can read more about standard and coloured anodising here.

Why Choose Us?

  • Hard anodising experience dating back to the 1960s.
  • Access to a world-wide hard anodising knowledge base.
  • In-house quality and testing team.
  • In-house corrosion testing facilities.
  • One to one million component capabilities, with the ability to do custom work.
  • A true ‘one-stop-shop’ for all your coating needs.


Aerospace Applications

Hard anodised components have excellent wear resistance, dry lubrication, longevity and electrical insulation characteristics.

Printing Press teflon coatings

Machinery Applications

Hard anodising is especially useful for abrasion resistance in high-speed machine parts such as printing presses and conveyors.


Cookware Applications

Hard anodising not only has the ability to withstand scratching from steel utensils, it also has excellent non-stick properties.

More on Hard Anodising

Thickness: 20-100 microns (subject to alloy).

Uniformity: Can vary in thickness.

Hardness: 400-600HV – Alloy 6082 (equates approximately to 65 to 70 Rockwell C)

Wear resistance: Excellent.

Gloss: Subject to chosen alloy and post processing.

Colours: Limited.

Flexibility: Anodic coatings are very hard and glass-like. With that said, they can crack when bent and thicker coatings can also craze when heated above approximately 80°C, which may effect corrosion resistance.

Toxicity: Anodic coatings are nontoxic and can be used for food contact applications.

Corrosion resistance: Subject to thickness and sealing process.

Chemical resistance: Anodised coatings have good resistance to mild acids but are attacked by alkali materials. This includes cement and lime mortars. Contact us to learn more about our special sealing processes that can greatly increase the resistance to alkali attack.

Recommended alloys: Purer grades of aluminium will anodise best. Other grades may result in discoloured anodic coatings due to the alloy components or restrict the formation of the film on the metal’s surface.

Standards: Due to the age of the anodising process, there are now long-established standards for anodic coatings both in Australia and internationally.

Conductivity: Anodic coatings are non-conductors. If used as part of an electrical circuit, provisions must be made for masking the component to prevent coating or removal of the coating post-processing.

Cost: Our charges will be subject to a number of factors such as volumes, processing conditions and rack requirements. Like many of our processes, the labour for racking, un-racking, inspection and packing play a very significant part in our overall charges. Please contact us to find out more.

Size limitations: Impreglon can hard anodise components up to 2800mm long, 800mm deep, and 350mm wide.

Recommended Uses

Hard anodising is a long-established and well-accepted engineering finish that finds use in many applications where high wear resistance is required. Before we process any work, we always provide a specification or a service requirement for the anodising so we can ensure our anodising meets all your needs, no matter how great or small.

Download our Hard Anodising Fact Sheet

Want more information, or prefer to download something to read later? No problem at all.
Here’s a downloadable .pdf document that covers off all of our service details so that you can read more or share it with a colleague.



Hard Anodising Case Study: Pentair Valve Bodies

When Pentair wanted the best coating for their world-class engineering, they came to Impreglon Australia for an innovative hard anodising and epoxy powdercoating solution.


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