Hard anodising is also known as hardcoat or Type III anodising. It is a specialised variation of the standard sulphuric anodising process. Hard anodising produces a significantly thicker and denser oxide layer on aluminium than the Type II version, typically ranging from 20 to 70 microns and in some cases up to 100 microns depending on the alloy. This enhanced layer dramatically improves both wear and corrosion resistance, making it ideal for high-performance engineering applications.
What Is the Hard Anodising Process?
The process relies on precise control of voltage, temperature and time to ensure a uniform coating across different component shapes. Around half of the oxide layer penetrates the metal surface, while the other half builds outward, so dimensional allowances are carefully calculated during design.
Who Can Perform It?
While Type II anodising is offered widely by the 40 or 50 metal finishing companies in the UK, hard anodising is categorised separately by Qualanod licensing, with no more than 25 businesses, such as https://www.poeton.co.uk/surface-treatments/anodising/hard-anodising/, holding Type III approval.
How Does It Affect Colour?
Although materials that have been treated with hard anodising can be dyed, the finish tends to be darker and less decorative than conventional anodising. Common colour options include natural, black, red, blue and purple. The coating may be sealed for greater corrosion resistance or left unsealed to optimise wear performance.
Compliance
Hard anodised surfaces are routinely tested to international standards such as ISO 10074 and MIL-PRF-8625 Type III. The result is a robust aluminium surface capable of withstanding demanding mechanical and environmental conditions across aerospace, defence and industrial applications.
