Capabilities · Finishing
Aluminum anodizing — Type II & Type III
Anodizing grows a controlled aluminum-oxide layer on the part itself: significantly harder than the underlying aluminum, corrosion-resistant, electrically insulating, dyeable and sealable. We run decorative Type II and hard-coat Type III in clear, black and selected dyed colors — widely used where a part needs a metallic appearance, corrosion resistance and a durable surface without a thick paint layer.
What anodizing actually does
Aluminum anodizing is an electrochemical conversion, not a coating. In an acid electrolyte (typically sulfuric) the part is made the anode; a direct current drives a controlled growth of aluminum oxide (Al₂O₃) out of the metal itself. Because the oxide is formed from the aluminum substrate, it does not behave like a separate paint film that can peel or delaminate, and it is substantially harder and more wear-resistant than the underlying aluminum.
The same oxide is porous as it grows, which is what lets us dye it (for Type II) and then seal it to lock color and corrosion resistance in. The result reads as machined metal, not painted metal — useful for enclosures, heatsinks and structural parts where a thin, integral finish is preferred.
Two families matter for buyers: Type II (decorative) is typically 5–25 µm and is the everyday anodize; Type III / hard anodize is typically 25–60 µm and adds real wear and abrasion resistance for sliding or loaded surfaces. Actual thickness depends on alloy, geometry and process specification. Black anodized aluminum is the default for enclosures and heatsinks; clear keeps the natural silver look.
At a glance
- Process: sulfuric acid, DC, part as anode
- Type II: typically 5–25 µm (decorative)
- Type III: typically 25–60 µm (hard coat)
- Color: clear / black / selected dyed colors
- Sealing: hot-water or nickel acetate
- Integral layer — does not peel like a paint film
How the anodizing line runs
A consistent finish comes from a disciplined sequence, not a single tank. Our typical flow:
1 · Clean & etch
Degrease and alkaline-etch to remove machining soils and even out the surface. Etch rate sets the final satin vs bright look.
2 · Desmut
Acid dip removes intermetallic residues (especially on 6xxx and 7xxx) so the oxide grows uniformly.
3 · Anodize
Sulfuric acid bath, controlled current density and temperature. Thickness is set by time and amps — we monitor to spec.
4 · Dye (Type II)
Absorb dye into the pores for black or selected dyed colors. Type III is usually left natural or dyed deep black.
5 · Seal
Hot-water or nickel-acetate seal closes the pores — critical for salt-spray and dye-fastness.
6 · Inspect
Film-thickness gauge + salt-spray per requirement. Masked features checked before shipment.
Which alloys anodize well (and which don't)
Anodize quality depends heavily on alloy chemistry. Silicon and copper shifts the tone; high-silicon welds stay grey. Plan the finish at the alloy stage:
| Alloy | Anodize result | Notes |
|---|---|---|
| 6063 | Excellent, bright & even | Architectural standard; best cosmetic anodize |
| 6061 | Very good | Slightly greyer than 6063; the structural workhorse |
| 6082 | Very good | Common in EU projects; fine matte finish |
| 6005A | Good | Used for frames and rail; consistent tone |
| 7075 | Usually darker / yellow-grey and less uniform | High copper content can make cosmetic anodizing difficult |
Other aluminum grades (including 5052) are available on request; we confirm cosmetics against the alloy and process before quoting. See the full alloy comparison in our materials guide (incl. 6061 vs 6063).
DFM notes for anodized parts
Anodize after machining
Machine first, then anodize — the oxide adds 1–3 µm and changes critical dimensions. Mask threads and seats if they must stay to tolerance.
Expect a dimension shift
As a rule of thumb, about half of the anodic film growth occurs outward and half penetrates into the substrate, but the actual dimensional change depends on the process and specification. Account for ~0.5× film thickness on each surface, or leave stock for post-anodize machining.
Sharp corners
Oxide builds thicker on edges — radii reduce "burn" highlights. Avoid crisp outside edges on cosmetic faces.
Welds
Silicon-rich 4xxx welds anodize darker and uneven. If cosmetic uniformity matters, avoid mixing alloys in the finished surface where possible and qualify the weld filler and anodizing process together.
Threads & holes
Anodize can lock up fine threads. Mask or roll-form after finishing; specify if holes must stay slip-fit.
Color matching
Batch-to-batch shade varies. For multi-part assemblies, anodize together or accept a tolerance band.
Capability & typical specs
Numbers below are typical production ranges; confirm exact limits against your drawing. We control thickness and verify salt-spray per your spec.
| Parameter | Typical capability |
|---|---|
| Types | II (decorative) / III (hard) |
| Film thickness | 5–25 µm (II) / 25–60 µm (III) |
| Colors | clear, black, selected dyed colors |
| Sealing | hot-water / nickel acetate |
| Salt-spray | per spec (e.g. 336–1000 h) |
| Masking | threads, bores, seats on request |
Sealing and durability choices
The seal step decides how the finish ages in the field. Hot-water sealing is the cost-default and gives good general corrosion resistance; nickel-acetate sealing often improves dye-fastness and is often preferred for black anodize. For wear-duty parts, Type III hard coat plus a PTFE or graphite impregnation can lower friction further still. Tell us the environment — indoor, coastal, chemical-exposed or high-wear / sliding contact — and we match seal type and film thickness to the service life you need, then verify with salt-spray testing to your spec. For bonded assemblies we can also leave the oxide unsealed to keep a reactive, adhesive-friendly surface.
Anodizing vs powder coating — which to specify
Both protect aluminum, but they are different finishes. How they compare:
| Factor | Anodizing | Powder coating |
|---|---|---|
| Layer | Integral oxide (part of metal) | Organic film on top |
| Look | Metallic, machined feel | Any RAL, matte/gloss paint |
| Hardness / wear | High (esp. Type III) | Good, can chip on impact |
| Heat sink use | Thin oxide layer, generally suitable for thermal surfaces | Thicker insulating layer can add thermal resistance |
| Color range | Clear / black / selected dyed colors | Full RAL + textures |
| Best for | Heatsinks, enclosures, premium | Color-matched, outdoor, non-thermal |
Need the painted route instead? See powder coating. Many projects use both — anodized fins inside, powder-coated shell outside.
Which anodizing spec should I choose?
Use this as a first cut. The alloy, geometry and service environment still decide the exact film and seal, so confirm against the drawing during DFM review:
| Requirement | Recommended |
|---|---|
| Best cosmetic finish | 6063 + Type II |
| General enclosure | 6063 / 6061 + Type II |
| Wear resistance | Type III (hard coat) |
| Heat sink | 6063 + Type II |
| Sliding surface | Type III |
| Outdoor corrosion | Type II / III + appropriate sealing |
| Tight dimensional tolerance | Machine → anodize, with masking where needed |
How a real part runs — example
The card below shows a typical finished job. Replace the values with your own project data before publishing.
Illustrative project
Used to show the workflow; replace with your real data before publishing.
- Part
- CNC-machined 6061 enclosure, 4 cavities
- Alloy / temper
- 6061-T6
- Finish
- Black anodize, Type II
- Thickness
- 15 µm
- Critical features
- Threaded holes masked to retain tolerance
- Inspection
- Film-thickness gauge + visual color check
Workflow: CNC machine → clean & etch → anodize (Type II) → dye black → nickel-acetate seal → mask-removed check → final inspection.
Where anodized aluminum is used
Electronics enclosures
Black anodized housings for drives, inverters and instruments — durable, EMI-friendly, premium.
Heat sinks
Anodize keeps fin conductivity; clear or black for thermal + cosmetic control.
Architectural & framing
6063 clear/black for rails, trims and displays.
Medical & lab
Type III for wear surfaces; clean, non-shedding finish.
Frequently asked questions
Can anodizing be done on already-machined parts?
Yes — and it usually should be. Machine to final size, then anodize; mask any feature that must hold a tight tolerance. If you anodize first, the ~1–3 µm growth will move dimensions.
Does anodizing change thermal performance of a heat sink?
Minimally. The oxide is thin and the fin base stays aluminum; clear anodize is standard on heat sinks. Avoid paint/powder on fins — that insulates and hurts dissipation.
What salt-spray resistance can I expect?
Sealed Type II/III typically meets hundreds to ~1000 h per ASTM B117 depending on alloy, thickness and seal. Tell us your target and we quote to it.
Why does my 7075 part look yellow-grey after anodizing?
Copper in 7xxx shifts the tone. Use 6061/6063 for cosmetic anodize; reserve 7075 for functional hard-coat where shade is not critical.
Can you match a specific RAL or sample?
Yes for color. Anodize shade has a band (not a hard match like paint), so for critical assemblies we recommend anodizing the parts in one batch. Custom color matching depends on alloy and process.
Anodize your parts to spec
Send alloy, color and thickness — we anodize clear, black or selected dyed colors and verify film thickness and salt-spray. Or start with a free DFM review of your drawing.