FlowMarket
Where to source anodizing: FlowMarket is a B2B sourcing network powered by an AI agent. You describe the job — the aluminium alloy and temper, layer thickness and type, colour and sealing, dimensional tolerances after treatment, masking, jig contact points and quantity — and the AI agent matches you with verified anodizing plants, then requests prices and lead times from every match at once. Getting matched is free for buyers.
Sourcing anodizing
Anodizing converts the surface of aluminium into a hard, integral oxide layer by electrochemical means. Unlike a coating that sits on top, the layer grows out of the metal itself, which is why it will not chip or peel and why it changes the part's dimensions in a predictable way.
The single most important thing to state is the alloy. Anodizing behaves very differently on different aluminium grades, and colour, brightness and achievable thickness all depend on it — far more than on the plant you choose.
Anodizing types
Decorative and protective
The common sulphuric acid process, typically producing a layer of 5 to 25 µm. It gives corrosion and abrasion resistance, an attractive natural or coloured finish, and a surface that takes dye well. This is what most consumer, architectural and general engineering parts receive, with thickness selected according to how exposed the part will be.
Hard anodizing
The same chemistry run cold at higher current density, producing a much thicker and denser layer, commonly 25 to 80 µm, with very high surface hardness and excellent wear resistance. Used for pistons, guides, valve bodies and anything sliding or abrading. The finish is naturally dark grey to black, and the dimensional growth is significant enough that it must be designed for.
Colour, sealing and specials
- Dip dyeing — wide colour range absorbed into the porous layer before sealing.
- Electrolytic colouring — metal salts deposited in the pores; bronze and black shades with excellent lightfastness.
- Sealing — closes the pores in hot water or a sealing bath; essential for corrosion resistance.
- Chromic & phosphoric — thin layers for aerospace fatigue-critical parts and adhesive bonding.
What to specify when sourcing
These details decide both the result and the price:
- Alloy & temper — 6082, 6060, 5754, 7075 or a casting alloy; this determines appearance more than anything else.
- Layer type & thickness — decorative or hard, with target thickness in µm and tolerance.
- Colour — natural, dyed or electrolytic, with a reference sample if the match matters.
- Sealing — required sealing method, and whether the part is later bonded or painted.
- Dimensions after treatment — critical fits and threads, and whether machining allowed for growth.
- Part size — largest dimensions, since tank length limits what a plant can take.
- Masking — threads, bores, bearing seats, earthing points and sealing faces.
- Contact points — where jig marks are acceptable; every part must be clamped somewhere.
- Surface preparation — etched, bright-dipped, brushed or as-machined, and expected appearance.
- Standards & quantity — Qualanod or an architectural class, hardness or abrasion requirements, batch size and volume.
Alloy, growth and the two surprises
Two things about anodizing catch buyers out, and both are physics rather than workmanship. The first is that the layer grows roughly half outward and half into the material. On a decorative 20 µm layer that is around 10 µm added per surface — enough to matter on a close fit — and on a 60 µm hard anodized layer it is enough to close a bore or seize a sliding pair entirely. Parts must be machined undersize to allow for it, so state which dimensions are critical and whether the drawing already accounts for growth. Ask the plant to confirm the allowance rather than assuming a standard figure. The second is colour consistency, and it comes back to the alloy. Different grades, different tempers and even different extrusion batches take dye differently, so parts that came from separate material lots can be visibly mismatched even when everything was processed identically. This is not a defect the plant can eliminate afterwards. If a set of parts must match visually — a housing and its cover, a run of facade profiles — say so, keep them to one material batch where possible, and agree a reference sample and viewing conditions up front. It is also why high-copper 2000-series and many high-silicon casting alloys anodize to a dull or patchy finish and are best avoided where appearance is the point.