Hard anodising aluminium with 50 to 125 microns thickness offers high wear resistance, corrosion protection, and fast UK/EU lead times.

When 336 hours of salt-spray testing just doesn’t suffice, engineers turn to hard anodising aluminium. Offering a rock-solid surface hardness of 60-70 Rc and coatings up to 125 μm thick, this process is the go-to for aerospace giants, Formula 1 teams, and medical OEMs demanding unmatched wear and corrosion resistance. Whether you’re specifying parts or sourcing a trusted UK/EU supplier, this guide cuts through the noise with precise specifications, real-world performance data, and lead times you can rely on. Ready to see why Type III hardcoat anodising outperforms every alternative? Let’s get right into it.

What Is Hard Anodising? Understanding Type III vs Type II vs Type I

If you’re wondering what sets hard anodising apart from regular anodising, you’re not alone. Hard anodising, also known as Type III sulphuric acid anodising, is a specialised process that creates a much thicker and harder oxide layer on aluminium compared to Type I or Type II anodising.

Here’s a quick breakdown of the three common anodising types:

Anodising Type	Typical Thickness	Process Temperature	Current Density	Acid Concentration	Hardness (HV)	Hardness (Rc)
Type I (Chromic Acid Anodising)	0.25-1.0 µm	45-55°C	Low (1-5 A/dm²)	Chromic Acid (0.15 M)	~200 HV	~45 Rc
Type II (Sulfuric Acid Anodising)	5-25 µm	18-22°C	Moderate (10-20 A/dm²)	Sulfuric Acid (15-20 wt%)	300-400 HV	50-55 Rc
Type III (Hard Anodising)	25-150+ µm	0-8°C (near freezing)	High (60-120 A/dm²)	Sulfuric Acid (15-20 wt%)	550-650 HV	60-70 Rc

How Hard Anodising Works Differently

• Temperature: Hard anodising runs much colder — near freezing (0-8°C) — compared to the warmer temps for Type II.
• Current density: It uses a higher electrical current, which speeds up oxide growth but requires precise control to avoid burning or uneven coating.
• Acid concentration: Both Type II and III use sulphuric acid, but the combination of low temperature and high current in Type III creates a dense, tough coating.

Microscopic Structure of Hard Anodised Aluminium

Hard anodising forms a thick oxide layer consisting of:

• A porous, hexagonal cell structure on the surface that can be sealed post-treatment to enhance corrosion resistance.
• A dense barrier layer approximately 50 µm thick that bonds directly to the aluminium substrate, providing incredible hardness and wear properties.

(Imagine a microscopic diagram showing hexagonal cells stacked like a honeycomb atop a solid, thick barrier layer.)

Hardness Comparison: What Does That Really Mean?

Hard anodised coatings have hardness values roughly 60-70 Rc, translating to 550-650 Vickers hardness (HV). To put that in perspective:

• Hard anodising is about 2-3 times harder than untreated aluminium.
• Comparable in hardness to some hardened steels, making it ideal for parts exposed to heavy wear and abrasions.

This makes hard anodising aluminium the go-to for parts like aerospace components, hydraulic pistons, and heavy-duty mechanical parts where durability counts.

Key Performance Advantages That Actually Matter

Hard anodising aluminium stands out because it delivers real, measurable benefits you can rely on.

• Wear Resistance: Thanks to a tough, dense surface, hard anodised parts show excellent durability. Lab tests like the Taber abrasion using a CS-17 wheel with 1000 g load prove it wears much slower than standard coatings.
• Corrosion Resistance: In real-world and lab tests (1000+ hours in Neutral Salt Spray per ASTM B117), hard anodised aluminium holds up strong, resisting rust and degradation far better than untreated or lightly anodised surfaces.
• Thermal Stability: This coating handles extreme temperatures, from as low as -196 °C (-321 °F) up to +400 °C (752 °F), without cracking or losing its protective properties, making it ideal for applications exposed to harsh heat or cold.
• Dielectric Strength: With insulation ratings between 800 and 1500 volts, hard anodised layers also provide excellent electrical resistance, useful for electronics and electrical components.
• Fatigue Resistance: Unlike standard anodising, which can reduce aluminium’s fatigue strength by about 30-50%, hard anodising only causes an 8-12% loss, meaning parts last longer under repeated stress.

These key advantages make hardcoat anodising the go-to finish for industries where durability, corrosion protection, and performance under tough conditions are non-negotiable.

Specification Cheat-Sheet for Hard Anodising Aluminium (MIL-A-8625 Type III)

When you’re looking at hard anodising aluminium under the MIL-A-8625 Type III standard, here’s the quick lowdown you need to know:

Class 1 vs Class 2

• Class 1: Non-dyed, clear finish for maximum corrosion resistance and natural aluminium look.
• Class 2: Dyed anodising, where colour options (usually black or other dyes) are added without compromising the tough coating.

Minimum Coating Thickness by Alloy

• 1xxx series (pure aluminium): Minimum 25 μm thickness – suitable for decorative and light wear applications.
• 7xxx series (high-strength alloys like 7075): Minimum 50 μm thickness – required to achieve full wear and corrosion resistance benefits.

Other common alloys such as 6xxx series generally aim for around 50 μm as well, balancing hardness and durability.

Sealing Options to Lock in Performance

• Hot Deionised (DI) Water: The standard sealing method, closing pores to enhance corrosion resistance.
• Nickel Acetate: Provides additional corrosion protection, especially in harsh environments.
• Dichromate Sealing: A traditional choice, now less common due to environmental concerns but still used for extreme corrosion resistance.
• PTFE Impregnation: For those requiring low friction and extra wear resistance, ideal for sliding parts.

Downloadable Specification Table

We have a detailed PDF specification sheet available to assist you in matching alloys, thickness, sealing, and colour options with your specific project requirements. It is branded and ready for customers—perfect for engineers and buyers who want all the facts in one place.

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This cheat-sheet keeps things straightforward, helping you select the right hardcoat anodising specifications quickly and confidently for your projects based in the United Kingdom.

Which Aluminium Alloys Perform Best for Hard Anodising?

When it comes to hard anodising aluminium, not all alloys are equal. Here is a quick overview of the top performers in the market:

• 2xxx Series (2024, 2011): These alloys can be tricky. They have good strength but require extra pre-treatments like careful cleaning and sometimes brightening to get the coating to adhere properly. Corrosion resistance after anodising isn’t as strong, so be cautious if the part faces harsh environments.
• 6xxx Series (6082, 6061): This is the sweet spot for hard anodising. These alloys balance machinability, strength, and excellent coating quality. They take well to the MIL-A-8625 Type III process, delivering durable, corrosion-resistant, and wear-proof finishes that suit most industrial and aerospace needs.
• 7xxx Series (7075, 7010): Want maximum hardness? Here you go. 7xxx alloys can push coating hardness to the limit with top-notch wear resistance. However, they’re sensitive to processing conditions — you’ll need precise control over the anodising parameters to avoid brittleness or cracking.
• Castings (A356, LM25): Casting alloys behave differently. They need a special, low-temperature anodising cycle to prevent thermal stress and ensure an even, strong hardcoat layer. Perfect for hydraulic parts and complex shapes but definitely a specialised process.

Picking the right alloy for your application is crucial. The 6xxx series usually offers the best combo of cost, performance, and ease of hard anodising for most manufacturing needs in the United Kingdom.

Thickness Guide – How Thick Should You Go?

Choosing the right hard anodising thickness depends on what you need from your aluminium parts. Here’s a quick guide:

• 25 μm: Good for decorative finishes and parts with moderate wear. Ideal if you want some protection without adding much thickness.
• 50 μm: The aerospace industry’s go-to standard. Offers solid wear and corrosion resistance for most applications.
• 75-100 μm: Perfect for heavy-duty parts like hydraulic pistons and gearbox housings where durability is key.
• 125 μm: For extreme abrasion situations, such as mining tools or equipment exposed to rough conditions.

Cost vs Thickness (2025 Real Pricing)

Thickness impacts cost directly. At vast, prices scale with coating thickness — expect about:

• Lower cost per dm² for thinner coatings (25 μm),
• Moderate pricing for 50 μm to 75 μm coatings,
• Higher prices on the 100 μm+ end due to longer processing and materials.

If you want to balance cost with performance, 50 μm usually hits the sweet spot, especially for United Kingdom-based aerospace and industrial uses. For really tough environments, investing in 100 μm or more pays off long-term.

Ask us for a custom quote with your part specs to see exact pricing in your volume.

Colour Options in 2025

Hard anodising aluminium offers several colour choices in 2025, balancing appearance with performance. Here’s what you can expect:

Colour	Notes
Natural silver-grey	Classic, no dye added
Jet black	Most popular choice, deep black
Olive drab	Defence use, muted green
Desert tan	Defence use, sandy beige
Blue	Limited availability, dye stability varies
Red	Limited, fading risk in some batches
Gold	Limited, used for special applications

Colour consistency is tight, with a guaranteed CIELAB ΔE less than 1.0, ensuring nearly identical shades batch to batch. This means your parts will look just as great years down the line.

If you need colours beyond black or natural, expect some variation, but we prioritise stable dyes to keep the finish looking sharp and reliable for United Kingdom applications.

Common Failures & How Vast Eliminates Them

When it comes to hard anodising aluminium, common issues like rack marks, burning on sharp edges, and uneven thickness can really spoil your parts. At Vast, we’ve nailed down solutions to keep your components flawless.

• Rack Marks: These annoying marks happen when parts touch the rack during anodising. Vast uses custom PTFE masking plus a 48-point contact system to spread out pressure evenly and prevent marking.
• Burning on Sharp Edges: Sharp edges tend to overheat and ‘burn’ during hard coating. Our pulse rectification technology controls the current flow to avoid overheating, delivering crisp, clean edges every time.
• Uneven Thickness: Variations in coating thickness weaken performance. Vast relies on a computer-controlled hoist and a slow 0.8 m/min ramp rate to ensure consistent anodising thickness across your entire batch.

Together, these smart tweaks mean you get a smoother, tougher hard coat every time—with far fewer rejects and headaches.

Hard Anodising Cost Calculator (2025 UK/EU)

Looking to budget your hard anodising aluminium project? Our 2025 UK/EU cost calculator makes pricing simple and transparent. Here’s what you can expect:

• Price per dm² breaks down by quantity:
  • 100 pcs: Higher rate per unit
  • 1,000 pcs: Moderate savings
  • 10,000 pcs+: Best bulk pricing
• Tooling charge covers setup costs—usually a one-time fee, depending on the complexity of your parts and rack design.
• Express 48-hour service comes with a surcharge, typically around 30% extra, if you need your parts fast.

For added convenience, we offer a live calculator widget on our site. Just input your part size, quantity, and turnaround needs to get an instant, tailored quote. This tool helps you compare costs right away and plan your project budget with ease.

Lead Times That Win Projects

When timing matters, hard anodising aluminium shouldn’t hold you back. We offer lead times tailored to keep your projects on track:

• Standard: 3-5 working days — perfect for most runs without rush fees.
• Express: 48 hours — add 30% for that quick turnaround when deadlines tighten.
• Emergency: 24 hours — a 60% surcharge gets you priority service on urgent jobs.

For example, a recent aerospace contract needed parts anodised overnight. We delivered within 24 hours without quality compromises, helping the customer avoid costly delays. Our flexible lead times mean you can plan confidently and meet your schedules, every time.

Sustainability & REACH Compliance

We’ve made hard anodising aluminium cleaner and greener. Since 2018, our entire process has been free of hexavalent chromium, one of the nastiest toxic chemicals traditionally used in anodising. This means safer products and a healthier environment.

On top of that, we recycle 98% of the water used in our anodising plants. That’s a huge cut in waste and a serious boost to sustainability. Our facility in Manchester even runs on solar power, reducing carbon footprint and energy costs.

So when you choose hard anodising with us, you’re not just getting top performance—you’re supporting eco-friendly practices that meet strict REACH regulations. It’s quality with a conscience.

How to Get a Quote in Under 2 Hours

Getting a hard anodising quote fast is easy when you know what to prepare. Just upload these four files:

• STEP file (3D model)
• Detailed drawing
• Quantity needed
• Your deadline

Once we receive your files, our engineers start immediately. They spend about 17 minutes reviewing specifications, feasibility, and costs to ensure the quote is accurate without delays.

After that, we guide you through the sample approval process with a clear flowchart showing each step—from initial sample, testing, to final sign-off—so you’re in control every step of the way.

This streamlined approach means you’ll receive a reliable, customised quote within 2 hours, helping you keep your United Kingdom-based projects on track without waiting around.