Clear (natural)
No colouring; the most durable and easiest to match. Satin-etched or brushed pre-treatment gives matt or directional looks.
Finished extrusions
Anodised Aluminium Extrusions and Profiles
Anodised aluminium extrusions are profiles, tubes, angles and channels whose surface has been converted into a hard, sealed layer of aluminium oxide by electrolytic treatment. The finish resists corrosion and wear, keeps a metallic look and cannot peel. Specify it by alloy, film class (for example AA15 or AA20 for architecture, or Type III hardcoat for wear parts), colour and sealing; Metline supplies anodised extrusions cut to length or machined to drawing for customers worldwide.
- Alloys
- 6060 · 6063 · 6463 · 6061 · 6082
- Film classes
- AA5 – AA25; hardcoat 25 µm +
- Colours
- Clear, champagne, bronze, black
- Standards
- ISO 7599 · AAMA 611 · MIL-A-8625
Why anodise aluminium extrusions?
Anodising makes the extrusion the anode in a sulphuric-acid bath. Current drives oxygen into the surface, growing a layer of aluminium oxide made of tiny hexagonal cells, each with a central pore. The pores can be filled with dye or metal salts for colour and are then sealed, leaving a dense, hard, transparent skin that is part of the metal.
Compared with paint or powder, anodising adds very little thickness, does not hide the metallic character of the aluminium, resists abrasion far better and does not chalk or peel. It is the traditional finish for window and curtain-wall profiles, shopfronts, handrails, machine-building frames, LED profiles and consumer products. Hard anodising (Type III) goes further, producing a thick, very hard coating for sliding and wearing parts.
The quality of the finish depends as much on the extrusion as on the anodiser. Alloy chemistry, die lines, press handling and the visible faces on the drawing all show through a transparent film. This guide covers the decisions that determine whether the finished profile looks and performs as intended.
Which extrusion alloys anodise best?
| Alloy | Anodised appearance | Strength | Typical use |
|---|---|---|---|
| 6060 | Very uniform, clear; excellent for colour | Moderate | Window and door systems, trims, furniture profiles |
| 6063 | Very good, clear and even | Moderate | Architectural profiles, LED channels, T-slot framing |
| 6463 | Bright and specular after chemical brightening | Moderate | Bright trim, appliance and automotive decorative profiles |
| 6061 | Good, slightly less even than 6063; good hardcoat base | High | Machined parts, structural frames, hardcoated components |
| 6005A | Fair to good; can look slightly grey | High | Structural profiles, rail and transport extrusions |
| 6082 | Fair; may show grain or grey tones on large flat faces | High | Structural sections where function matters more than looks |
| 7xxx / 2xxx | Yellowish (7xxx) or poor and patchy (2xxx) | Very high | Functional and hardcoat aerospace parts, not decorative |
For decorative work, 6060 and 6063 are the safe choices: low iron and controlled magnesium and silicon give a clear film with consistent colour. Strength-driven alloys such as 6082 and 6005A anodise well for protection, but large visible faces may show streaks or grain. When a project needs both strength and appearance, discuss the visible faces with the extruder and approve samples before production.
Do not mix alloys or tempers on one visible assembly: the same anodising cycle gives different tones on different alloys.
Film thickness classes, Type II and Type III
| Class / type | Film thickness | Standard | Typical service |
|---|---|---|---|
| AA5 – AA10 | 5 – 10 µm | ISO 7599 | Interior decorative profiles, furniture, electronics |
| AA15 | 15 µm minimum average | ISO 7599 | Normal exterior exposure; most architectural work |
| AA20 | 20 µm minimum average | ISO 7599 | Polluted urban or moderate coastal exposure |
| AA25 | 25 µm minimum average | ISO 7599 | Severe marine and industrial exposure, high abrasion |
| AAMA 611 Class II | 10 – 18 µm (0.4 – 0.7 mil) | AAMA 611 | Residential and light commercial architecture (US) |
| AAMA 611 Class I | 18 µm (0.7 mil) and above | AAMA 611 | Commercial architecture and exteriors (US) |
| Type II (sulphuric) | Typically up to about 25 µm | MIL-A-8625 | Decorative and protective engineering finishes |
| Type III (hardcoat) | Commonly 25 – 75 µm; around 50 µm typical | MIL-A-8625, ISO 10074 | Wear surfaces, slides, pistons, fixtures |
Film growth affects dimensions. A conventional sulphuric film grows partly into the metal and partly outwards, so the part gains roughly one third of the film thickness on each surface. Hardcoat grows about half outward and half inward, so a 50 µm hardcoat adds about 25 µm per face, or 50 µm on a diameter. Machine critical fits allowing for this, or mask them.
Hardcoat is usually left natural (grey to bronze-black, depending on alloy and thickness) or dyed black. It is hard and wear-resistant but more brittle than Type II, so avoid it on parts that will be bent after anodising. For hardcoated bar stock, see our hard anodised bar guide.
Colouring and sealing anodised profiles
Electrolytic (two-step) colour
Tin or other metal salts are deposited at the base of the pores to give champagne, light to dark bronze and black. Very lightfast; the standard for exterior architecture.
Organic dyes
Immersion dyes give black, gold, red, blue and many other colours. Excellent indoors; lightfastness varies outdoors, so check dye data.
Hot-water sealing
Boiling deionised water hydrates the pore walls and closes them. Robust and preferred by many specifiers for exterior and coastal work.
Mid-temperature sealing
Nickel acetate or additive-based seals at lower temperature, saving energy and reducing smut; widely used with good control.
Cold sealing
Nickel fluoride-based seals at near-room temperature followed by ageing or a warm-water rinse. Needs careful control to achieve full sealing.
Sealing is what turns a porous film into a durable one. An unsealed or poorly sealed film stains easily and loses corrosion resistance. Quality schemes verify sealing with admittance (ISO 2931), dye-spot (ISO 2143) or acid-dissolution (ISO 3210) tests. For colour, specify by named shade and approve limit samples showing the lightest and darkest acceptable tones; a ΔE tolerance measured by spectrophotometer is common on large projects.
Choosing the film for the environment
| Exposure | Recommended film | Type | Notes |
|---|---|---|---|
| Indoor, dry | AA10 – AA15 | Type II | AA5 – AA10 is enough for purely decorative interior parts |
| General outdoor | AA15 – AA20 | Type II | Clear or electrolytic colours; good sealing essential |
| Coastal, high salt or industrial | AA20 – AA25 | Type II | Hot-water sealing preferred; plan regular washing |
| Heavy wear, sliding contact | 25 µm and above | Type III hardcoat | Check dimensional growth and fit; avoid post-bending |
Even a good anodised film needs simple care outdoors: periodic washing with water and a neutral detergent removes salt and pollutant deposits that would otherwise concentrate on the surface. Avoid alkaline cleaners and mortar or concrete splashes, which attack anodic films, and protect profiles on site until construction trades are finished.
Designing and specifying extrusions for anodising
- Mark visible faces on the drawing. Extruders orient die lines, handling and racking contacts away from them.
- Allow for rack marks. Each profile needs an electrical contact point, which leaves a small unanodised mark; agree where it may be (usually an end that will be cut off or hidden).
- Avoid deep blind slots and enclosed cavities where solutions are trapped and film cannot grow evenly.
- Keep wall thicknesses as uniform as practical: thick-to-thin transitions can show as tone differences after etching.
- Specify tolerances to EN 755-9 or EN 12020-2 (precision 6060/6063 profiles) or ANSI H35.2 for ASTM orders, and allow for film growth on critical fits.
- Specify film thickness measurement: eddy-current per ISO 2360 or ASTM B244, measured on significant surfaces.
- Plan fabrication order. Cut, drill and machine before anodising where the finish must cover everything; otherwise seal or accept bare cut edges.
Lengths are typically around 6 m, the common length for anodising racks and transport; other lengths are possible depending on the line. Profiles can be supplied cut to precise lengths and CNC-machined (drilled, tapped, milled) before or after anodising to suit the part.
Common anodising defects and how they are prevented
| Defect | Typical cause | Prevention |
|---|---|---|
| Colour variation between profiles | Different alloy lots, etch time, film thickness or bath condition | Single-alloy supply, controlled cycles, limit samples and ΔE checks |
| Streaks and banding | Die lines, uneven quench, alloy segregation, poor agitation | Good die and press practice, uniform quench, agitation and current control |
| Burning | Excess local current density on edges or poor contact | Correct racking, contact area and ramped current |
| Pitting and spots | Contaminated rinse water, chloride, residues before anodising | Clean cascade rinses and monitored water quality |
| Powdery or soft film | Over-hot bath or excessive time | Bath temperature and time control |
| Poor sealing (staining) | Low seal temperature or time, contaminated seal | Sealing tests per ISO 2931 / ISO 2143 on every batch |
| Exposed grain or spangle | Coarse recrystallised grain at the surface | Alloy and extrusion temperature control; avoid deep etching |
A full catalogue of colour defects, with causes, is in our insight article on anodising colouring defects.
Standard and custom shapes available anodised
Angles, channels and tees
Equal and unequal angles, U and C channels, tees and flat bar in 6063 or 6061 for trims, edging and light framing.
Tubes
Round, square and rectangular tube for handrails, furniture and frames.
T-slot framing
Clear-anodised T-slot profiles in common 20, 30, 40 and 45 mm series for machine building and automation.
Architectural profiles
Window, door, curtain-wall and shopfront sections anodised to architectural film classes.
Custom profiles
Profiles extruded from your die drawing, anodised in the colour and class you specify.
Hardcoated parts
Machined components and bar hardcoated for wear resistance.
Ordering checklist
- Profile
- Standard shape and size, or die drawing with visible faces marked
- Alloy and temper
- e.g. 6063-T5, 6061-T6, 6463-T5 for bright finish
- Finish
- Film class or type, colour, pre-treatment (etched, brushed, bright) and sealing
- Length and processing
- Stock or cut lengths, machining before or after anodising
- Documents
- EN 10204 3.1 mill certificate and anodising test report (thickness, sealing)
- Delivery
- Interleaved and film-protected bundles in export cases; EXW, FOB, CIF or DAP
References and standards
- ISO 7599 – Anodizing of aluminium and its alloys: decorative and protective anodic oxidation coatings
- AAMA 611 – Voluntary Specification for Anodized Architectural Aluminum
- MIL-A-8625 – Anodic Coatings for Aluminum and Aluminum Alloys
- ISO 10074 – Specification for hard anodic oxidation coatings on aluminium and its alloys
- EN 755-9 – Extruded rod/bar, tube and profiles: tolerances on dimensions and form for profiles
- QUALANOD – Specifications for the quality label for sulfuric acid-based anodizing of aluminium
Anodised (anodized) aluminium extrusions: frequently asked questions
Which alloy is best for anodised extrusions?
6063 and 6060 give the most uniform, clear anodised finish and are the standard for architectural and decorative profiles. 6463 is used for bright, specular finishes; 6061 is a good choice for strength and hardcoat.
What anodising thickness do I need for outdoor profiles?
AA15 for normal exterior use, AA20 for polluted or moderate coastal sites and AA25 for severe marine exposure. In the US, AAMA 611 Class I (18 µm and above) is specified for commercial exteriors.
What is the difference between Type II and Type III anodising?
Type II is conventional sulphuric anodising, usually up to about 25 µm, used for decorative and protective finishes in many colours. Type III hardcoat is thicker (often around 50 µm) and much harder, used for wear resistance, with a limited colour range.
Does anodising change the dimensions of an extrusion?
Slightly. Conventional films add roughly one third of their thickness to each surface; hardcoat adds about half. A 50 µm hardcoat increases a diameter by about 50 µm, so critical fits should be machined to allow for it or masked.
Can anodised profiles be cut and drilled after finishing?
Yes, but cut ends and holes will be bare aluminium. Indoors this is usually acceptable; outdoors, hide or seal them, or machine before anodising.
Does Metline supply anodised extrusions internationally?
Yes. Metline supplies standard and custom anodised aluminium extrusions, cut to length or machined to drawing, with mill certificates, anodising test reports and export packing to customers worldwide.
Need anodised aluminium extrusions?
Send the profiles, alloy, film class, colour, lengths and quantities. We will reply with availability, samples and a delivered price.
