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Anodize Type II (sulfuric)
Type II anodize is an electrochemical process that grows a porous aluminum oxide layer, 0.0002–0.001 in (5–25 µm) thick, from the part surface in sulfuric acid. The pores take dye for black, red, blue and other colors, then are sealed. It adds corrosion and wear resistance, is electrically non-conductive, and is specified to MIL-A-8625 Type II, Class 1 (clear) or Class 2 (dyed).
- Applies to
- Wrought aluminum alloys, best on 6061, 6063, 5052 and 7075; poor on high-silicon die castings such as A380
- Adds
- 4 days
- Cost
- Low
Colors
- Clear
- Black
- Red
- Blue
- Gold
- Green
- Gray
- Violet
Specs
| Coating thickness | 0.0002–0.001 in (5–25 µm); 0.0004–0.0007 in (10–18 µm) common |
|---|---|
| Dimensional growth | Roughly one-third to one-half of the coating builds above the original surface |
| Corrosion resistance | 336 h ASTM B117 salt spray, sealed, per MIL-A-8625 |
| Electrical | Non-conductive; mask grounding and contact points |
| Sealing | Hot DI water, nickel acetate or mid-temperature seals |
| Color | Clear (Class 1) or dyed (Class 2) |
Call out on the drawing
- MIL-A-8625 Type II, Class 1 (undyed) or Class 2 (dyed)
- AMS 2471 (undyed) / AMS 2472 (dyed)
- ASTM B580 (anodic oxide coatings on aluminum)
- ISO 7599
Questions
How thick is Type II anodize?
MIL-A-8625 allows 0.00007–0.001 in (1.8–25 µm), and most parts get 0.0004–0.0007 in (10–18 µm). Dyed black needs enough thickness, usually 0.0004 in (10 µm) or more, for a deep, even color.
Does anodizing change part dimensions?
Yes, slightly. About one-third to one-half of the oxide builds up on each surface, so a 0.0006 in coating grows each face roughly 0.0002–0.0003 in and a diameter twice that. Mask or pre-size tight bores and threads.
Is anodized aluminum electrically conductive?
No. Anodize is an insulator. Mask areas that need grounding or electrical contact, or specify chem film (MIL-DTL-5541 Class 3) for conductive corrosion protection.
Will black anodize fade outdoors?
Organic dyes can fade in long UV exposure, reds and blues especially. For outdoor parts, specify lightfast dyes, two-step electrolytic coloring for bronze and black, or clear anodize.
Other finishes on these processes
Price it with this finish.
The builder adds lot charges, per-part cost and lead time for the finish you pick.