Anodising of Aluminium
Type II decorative and Type III hard anodising for machined and laser-cut aluminium parts in Egypt, the UAE and Saudi Arabia
Anodising is an electrochemical process that grows a controlled aluminium-oxide layer on the surface of an aluminium part. Unlike paint, the layer is part of the metal itself, so it cannot peel or flake. Type II (sulphuric acid) anodising produces 5-25 µm for decorative and light corrosion protection; Type III hard anodising produces 25-50 µm for wear resistance. CutLinq arranges anodising as a finishing step after CNC machining, laser cutting or bending, through suppliers in Egypt, the UAE and Saudi Arabia.
This page explains which alloys anodise well, how the oxide layer affects your tolerances, which colours are stable in Gulf sunlight, and what to specify on a drawing so the supplier applies the correct thickness and sealing.
How anodising works
The part is cleaned, etched in caustic soda, then immersed in a sulphuric acid electrolyte at 18-22 °C for Type II or at 0-5 °C for Type III, with the part connected as the anode. Current density of 1.2-1.8 A/dm² (Type II) or 2.5-4 A/dm² (Type III) drives the growth of a porous oxide layer. The pores are then filled with dye if a colour is required and sealed in hot water or nickel acetate to close them.
Roughly half of the oxide thickness grows into the base metal and half grows outward. A 20 µm Type II layer therefore adds about 10 µm per surface; a 50 µm hard layer adds about 25 µm per surface, which matters on bores and threads.
| Type | Thickness | Hardness (HV) | Main use |
|---|---|---|---|
| Type II decorative | 5-15 µm | 200-300 | Appearance, light indoor protection |
| Type II architectural (AA20-AA25) | 20-25 µm | 250-350 | Exterior facade, coastal exposure |
| Type III hard | 25-50 µm | 400-500 | Sliding parts, pistons, tooling |
| Type III hard + PTFE | 30-50 µm | 400-500 | Low friction, food and packaging machinery |
Which alloys anodise well
Wrought alloys with low copper and silicon content give the clearest, most uniform finish. Cast alloys and high-copper 2xxx or 7xxx series anodise but produce a grey or brownish tint and a softer layer.
For a matched colour across an assembly, order all parts in the same alloy and, if possible, the same batch of material. 6061-T6 machined parts and EN AW-5754 bent sheet will look visibly different after the same black dye.
| Alloy (EN / common) | Type II result | Hard anodising | Note |
|---|---|---|---|
| EN AW-6063 (6063) | Excellent, clear | Good | Best for architectural profiles |
| EN AW-6082 / 6061-T6 | Good, slight yellow-grey | Good | Standard for machined parts |
| EN AW-5754 / 5052 | Good, uniform | Fair | Sheet metal, bent parts |
| EN AW-7075-T6 | Fair, greyish | Good | Layer slightly softer |
| EN AW-2024 | Poor, brown tint | Fair | Avoid for decorative use |
| Cast AlSi10Mg | Poor, dark and patchy | Poor | Consider powder coating instead |
Colours and sealing for MENA climates
Organic dyes (red, blue, green, gold) fade in direct UV, and rooftop temperatures in Riyadh or Dubai reach 70 °C in summer. For exterior parts specify clear (natural), black, or electrolytic two-step bronze and champagne, which are inorganic and UV-stable. Black organic dye holds well in shade but will turn brownish after 2-3 years on a south-facing facade.
Sealing is what stops Gulf salt air and Cairo dust from penetrating the pores. Hot-water sealing at 96-100 °C for 2-3 minutes per µm is standard; nickel acetate sealing improves salt-spray resistance to over 336 hours per ISO 9227 and is the better choice for coastal projects in Alexandria, Jeddah or Abu Dhabi.
- Clear (natural): most consistent, shows machining marks, UV-stable
- Black: most requested; specify inorganic or two-step for exterior
- Bronze and champagne (electrolytic two-step): UV-stable, architectural
- Red, blue, gold, green (organic dye): indoor only
- Hard anodising natural: grey to dark grey depending on alloy and thickness, colour not controllable
Dimensional effect and tolerances
Because the layer grows into and out of the surface, machined dimensions shift. For Type II at 15 µm the change is negligible on most parts, but a hard-anodised H7 bore of 20 mm will close by 40-50 µm and go out of tolerance. Either machine the bore 0.05 mm oversize before anodising or mask it.
Threads are usually masked, or tapped after anodising. Small blind holes below 3 mm can trap electrolyte; ask for a rinse specification or design them as through-holes.
Preparation and finish options
The anodised surface reproduces whatever is underneath it. A machined part with visible tool paths will show them; a bead-blasted part gives a uniform matt finish that hides minor scratches and is the standard for enclosures and consumer products. Brushing (grain 180-240) gives the linear satin look used on nameplates and audio panels.
Every part needs a contact point for the electrical rack, which leaves a small unanodised mark of 2-5 mm. Tell CutLinq which surface may carry the rack mark, or design a hidden hole or edge for it.
Design tips
- Specify thickness on the drawing: Type II 10-15 µm for indoor, 20-25 µm for exterior, Type III 40-50 µm for wear surfaces.
- Allow for growth: machine hard-anodised bores 0.04-0.05 mm oversize and shafts 0.04-0.05 mm undersize, or mask them.
- Keep blind holes above 3 mm diameter and below 5x diameter depth to allow rinsing.
- Use the same alloy for all parts in a visible assembly; never mix 6061 and 5754 in one colour set.
- Bead-blast before anodising (Ra 1.5-3 µm) for a uniform matt look that hides handling marks.
- Choose clear, black inorganic or bronze two-step for anything exposed to Gulf sun; keep organic colours indoors.
- Mark the allowed rack-contact location on the drawing, or add a 3 mm hole in a hidden flange.
Applications
| Industry | Example parts | Typical material |
|---|---|---|
| Electronics and enclosures | Heat sinks, front panels, bezels | 6061-T6, 6063 |
| Architecture and facades | Louvres, cladding brackets, handrails | 6063, EN AW-5754 |
| Signage | Letters, nameplates, backing plates | EN AW-5754, 6063 |
| Machinery and automation | Guide rails, pistons, cam plates (hard) | 6082, 7075-T6 |
| Food and packaging | Chutes, slides, guides with PTFE hard coat | 6082, 6061-T6 |
| Automotive and motorsport | Brackets, spacers, cosmetic covers | 6061-T6, 7075-T6 |
| Solar | Frame clamps, junction box covers | 6063, 6005A |
Pricing and lead time
Anodising is priced per batch and per rack load, so three cost drivers dominate: the total surface area and part size (a 600 mm panel occupies a rack position that could hold twenty small brackets), the type and thickness (hard anodising at 50 µm costs roughly 2-3 times Type II at 15 µm because of the chilled electrolyte and long cycle), and the colour and masking work (clear is cheapest, two-step bronze costs about 30-50% more, and every masked bore adds manual labour). Realistic lead time for anodising alone is 3-5 working days; combined with CNC machining of the part, plan 7-12 working days from order to delivery in Cairo, Dubai or Riyadh.
Frequently asked questions
Yes, provided it is a wrought alloy and free of steel inserts, welds with dissimilar filler, or heavy oxidation. Send photos and the alloy designation; parts of unknown alloy are anodised at your risk of colour variation.
Upload your STEP or DXF file with the anodising type, thickness and colour noted, and receive a binding quote within 12 hours.