Enhance Your Aluminium Parts: Anodising Benefits & Process Guide

If you're working with aluminium parts and need a finish that improves durability, corrosion resistance, and appearance, anodising will help you finish strong, literally.

What Is Aluminium Anodising?

Aluminium anodising is a surface treatment that forms a tough, durable oxide layer on the surface of aluminium. This layer boosts corrosion resistance, improves wear properties, and allows for colour finishes.

It works by enhancing aluminium's naturally occurring oxide layer through an electrochemical process. This thickened layer is tightly bonded to the surface, making it harder, less conductive, and more resistant to damage over time.

Unlike coatings or paints that sit on top of the surface, anodising changes the metal itself, so it won't peel or chip. This layer is porous before sealing, which allows it to absorb dyes, giving parts a decorative or branded finish that holds up better than paint or powder coating.

How Does Aluminium Anodising Work?

Aluminium anodising is an electrochemical process that works by altering a metal surface to make it more durable and corrosion-resistant.

Picture a part made from aluminium, like a bike pedal. During anodising, the first step is to submerge the pedal in a diluted sulphuric acid bath. Then an electric current is run through the solution. The aluminium pedal becomes the anode—the positively charged electrode—which is where the term 'anodising' comes from. In this setup, the anode attracts negatively charged oxygen ions, which bond with the aluminium surface to form a hard, protective layer of aluminium oxide.

Because the oxide layer is porous, it can soak up dye when you want to add colour. How much colour it holds depends on the dye strength, temperature, and how long the part stays in the bath. A final sealing step closes those pores to lock everything in.

This results in a hard, non-conductive finish that stands up to friction, moisture, and daily wear and tear.

What Are the Steps of Aluminium Anodising?

The anodising process follows a progressive series of steps designed to prepare, strengthen, and protect the aluminium surface.

Pre-treatment: The part is cleaned and degreased. It’s usually etched to create a smooth, uniform finish.
Anodising: The part is dunked in a sulphuric acid bath and zapped with an electric current. This builds up the aluminium oxide layer.
Colouring (optional): If you want colour, in this step the porous oxide layer gets soaked in a dye bath to absorb pigment. The longer it stays in, the deeper the colour.
Sealing: Finally, the part is sealed to close the pores. This locks in colour and boosts wear and corrosion protection.

What Are the Different Types of Aluminium Anodising?

There are a few types of aluminium anodising used in manufacturing, and the right one for your project depends on the finish you want and how tough the part needs to be:

Type I (chromic acid anodising): This one creates a very thin layer, good for aerospace parts that need light protection. It’s not as tough as others and is used less often today because of environmental restrictions.
Type II (sulphuric acid anodising): Also called decorative anodising. It builds a thicker oxide layer that can hold dye, so you can add colour. It’s common for everyday products and general engineering work.
Type III (hard coat anodising): Hard coat anodising forms a much thicker, harder layer that stands up to wear and corrosion. You’ll find it on parts in factories, ships, or aircraft.
Other variants: There are also niche options like phosphoric acid anodising or plasma electrolytic oxidation (PEO), but these are mostly used in research or specialised applications.

What Anodising Services Does Protolabs Europe Offer?

We offer Type II (decorative) and Type III (hard coat), two of the most common types of aluminium anodising for CNC-machined parts. These finishes differ in performance and application:

Type	Layer Thickness	Resistance	Appearance	Cost	Standards
Type II	1.8–25 µm	Good	Black or clear, can be dyed	Lower	ISO 7599
Type III	13–100 µm	Very good	Typically left uncoloured	Higher	ISO 10074

Protolabs Anodising Service Highlights

Lead times from 5 days
ISO and RoHS compliance
Instant online quoting
Support for aluminium alloys 6082-T651, 7075-T651 and 7075-T7351
Smooth or matte bead-blasted finishes available
Threaded hole blanking or plugging (note: masking of specific regions is not currently available)

To explore our full capabilities, visit our anodising service page.

Advantages of Aluminium Anodising

Aluminium anodising has a lot of benefits. Here’s why engineers keep coming back to it:

Corrosion resistance: The oxide layer acts like a shield, helping parts survive in tough conditions like offshore, aerospace, and industrial settings.
Durability: The surface is scratch-resistant and tough. Great for parts that see regular use or handling.
Electrical insulation: The anodised layer is non-conductive, which helps prevent short circuits and improves safety when parts are near wiring or electronics.
Clean look: Clear or black finishes look professional and polished. Ideal when parts are customer-facing.
Low maintenance: Anodised parts are easier to clean and less likely to wear down or flake over time.
Strong dye retention: When dyed, the finish resists fading better than paint or powder coatings.
Better adhesion: Anodised surfaces also improve adhesion for paint or glue, which is useful for downstream assembly.
Repeatability: The process delivers consistent results across batches.

Common Applications of Aluminium Anodising

You probably come across anodised aluminium on a daily basis, from phones and tools to bike parts and even cookware. When you notice a sleek, matte, often coloured aluminium finish, there’s a good chance it’s anodised. It’s especially popular where parts need to be tough, lightweight, and resistant to the elements. That’s why some industries, like aerospace or marine, rely on it more than others.

Aerospace: You’ll find anodised aluminium on aircraft brackets and housings because it is built to handle high-stress environments.
Consumer electronics: That premium, coloured phone or laptop casing? Likely anodised. It resists fingerprints and holds colour over time.
Medical: Anodised tools and housings are tough, cleanable, and safe for repeated sterilisation.
Marine: If it’s made of aluminium and lives near salt water, anodising helps it last. Think boat fittings and enclosures.
Industrial equipment: In factories or harsh outdoor environments, anodised parts resist wear and don’t chip like paint might.

Where to Learn More

Feel like you’ve just scratched the surface of anodising? Add another layer to your learning with these resources:

Insight: What is anodising? A video explainer that shows how the process works and when to use it.
Anodising vs. Electroplating: Weighs the pros and cons of two popular metal finishes.
A Tough Part: Practical information and design advice on coating thickness, jigging, and choosing between decorative or hard coat finishes.

If you’re exploring other ways to finish your machined parts, browse our full CNC finishing services lineup.

Frequently Asked Questions About Aluminium Anodising

How thick is the anodised layer?

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Decorative (Type II) anodising typically builds a layer between 1.8–25 µm thick. Hard coat (Type III) anodising creates a much thicker layer, ranging from 13–100 µm. The exact thickness depends on the time in the bath, current density, and alloy used. Find out more on our service page.

Does anodising affect part dimensions?

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Yes. The oxide layer typically grows approximately 50% into the surface and 50% outward. Design tolerances should allow for this growth, especially on critical features.

Which aluminium alloys are suitable for anodising?

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We currently offer anodising for 6082-T651, 7075-T651 and 7075-T7351. These alloys respond well to anodising and are commonly used in engineering applications. Cast aluminium alloys, especially those with high silicon content, are not recommended because they don’t produce a consistent or high-quality anodised finish.