Hard Anodising

Your Guide to Hard Anodising

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High quality precision machined components

Specialising in intricate, tight tolerance work

Extensive experience and high customer satisfaction

Penta Precision is able to offer hard anodising as part of our one-stop machining service in the UK.

As well as our own machining expertise, we are able to access our network of approved quality suppliers for the finishing of your parts, saving you the time and effort and helping to streamline your supply chain.

Customers turn to us when they have had quality and delivery issues with their existing suppliers and need a reliable machining partner.

Why Choose Hard Anodising?

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Excellent wear resistance and increased durability
Close tolerance control
Resistant to high temperatures

Increased corrosion resistance
Provides electrical insulation
Aesthetically pleasing finish – from clear to light grey through to black

Hard Anodising

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Hard Anodising Process

Hard anodising is very similar to sulphuric acid anodising. Using a higher acid concentration, it is processed at a solution temperature of 0°C with a significantly higher voltage being applied.

A thicker oxide layer and therefore increased corrosion resistance, electrical insulation and increased wear resistance compared to standard sulphuric anodising.

As aluminium “oxidises” (the natural reaction between air and aluminium, it produces a loose dry white powder, aluminium oxide. Sulphuric acid anodising is an electrolytic process using higher voltage (DC current) and a higher concentration sulphuric acid electrolytic solution causing oxidation of the aluminium surface to form thicker “harder” layers of aluminium oxide under controlled conditions.

The passing of the current liberates high volumes of Oxygen at the surface of the aluminium thus aiding controlled formation of the oxide layer. These processes do not produce a coating but are a conversion of the surface aluminium to aluminium oxide and are therefore metallurgically bonded.

The techniques produce a tight but porous layer which because it is porous requires a sealing process to close the pores and prevent further natural attack on the aluminium.

Sealing is carried out by immersing the component in near boiling de-mineralised water, which if required can have small quantities of other chemicals, such as Nickel acetate or sodium dichromate to further enhance corrosion resistance.

Most Common Specifications:

ISO 10074
MIL-A-8625 Type III
Def Stan 21-5 2-3
JP249
ASTM B580 Type A

Components, Applications and Industries

Hard anodising is often used in aerospace and automotive components where the hard wearing properties are most beneficial. Hard anodised aluminium can also be found in architectural and construction applications due to resistance to weathering. General engineering applications also benefit from hard anodising.

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Notes for Designers

Anodising is somewhat of an "artisan" practice rather than a precision process. As such, although there are defined controlled processes that a compotent processor will run, there are certain factors that will effect results and may be out of their control.

For example, colour matching can be very difficult when it comes to hard anodising. Some factors can be controlled such as layer thickness and the conditions at which the anodising are done. However, there are some factors beyond the control of the anodising engineer such as thermal history.

Material Grades

Material Grades for Hard Anodising

Hard Anodising gives best results on 6061 or 6082 aluminium alloys but any 6000 or 7000 series aluminium is generally suitable for hard anodising. 1000, 2000 and 5000 series can be hard anodised but with some compromises. Please call our team to discuss.