hard anodising

Hard Anodising

Aluminium Conversion Coatings

The Anochrome Group has two sites which provide surface conversion coating for aluminium; these coatings can be split into three basic areas as shown below, although all the different types of conversion coating have many different sub types with specific properties of colours.

The Bloxwich based facility of Anochrome Technologies specialises in automated high volumes with the ability to accept larger parts, whilst the Farnborough facility offers more of a range of different anodising or alochroming methods.


Anodising is an electrochemical process that converts the metal surface by a controlled growth or aluminium oxide (bauxite) at predetermined current densities. Thick coatings are normally porous, so a sealing process is often needed to achieve corrosion resistance. Anodised aluminium surfaces, for example, are harder than aluminium but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from ageing and wear.


Passivation is the process of making a material “passive”, usually by the deposition of a layer of oxide on its surface. In air, passivation affects the properties of almost all metals–notable examples being aluminium, zinc, titanium, and silicon. In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide that is a few nanometres thick.

Pure aluminium naturally forms a tough resistant oxide, almost immediately, that protects it from further oxidation in most environments. Aluminium alloys, however, offer little protection against corrosion.


Alocrom is a chromate conversion coating chemically applied to aluminium, which provides corrosion protection. It is also applied prior to painting or powder coating and is used when protection and/or electrical conductivity is required.

More details can be found on the downloadable PDF fact sheets.

We understand that a tailored approach to hard anodising is essential to your business. You can email us via the Contact page to discuss your individual requirements with an expert. We are also happy to provide you with further information on the hard anodising process by email, or alternatively you can call us on 01902 397333.