Anodizing, conversion & passivation · finish comparison
Anodizing Type II vs Chromic Acid Anodizing Type I
Anodizing Type II and Chromic Acid Anodizing Type I are both anodizing & conversion coatings finishes; type II anodize is the lower-cost option ($$).
Anodizing Type II
Anodizing & conversion coatings · $$ · instant quote
Type II sulfuric anodizing converts aluminum into a porous aluminum-oxide coating that can be clear or dyed.
Chromic Acid Anodizing Type I
Anodizing & conversion coatings · $$$
Type I and low-voltage Type IB chromic-acid anodizing form thin, corrosion-resistant oxide on aluminum with less fatigue penalty than thick sulfuric anodize.
When to choose which
Choose Type II anodize
Choose Type II anodize when decorative color and broader availability matter.
- Provides a hard 200–400 HV oxide
- Supports clear and many dyed colors
- Sealed coatings meet a 336-hour ASTM B117 requirement under MIL-A-8625
Choose Type I anodize
Type I anodize is the pick when its strengths below matter more than Type II anodize's.
- Thin 0.5–7.5 µm oxide limits dimensional change
- Lower fatigue debit than thick sulfuric or hard anodize
- Good corrosion protection after sealing
What the numbers say
- Type II anodize is the lower-cost option ($$).
- Type I anodize is the thinner coating (0.5–7.5 µm), so it disturbs tight fits less.
Scores side by side
Each score is 0–100 against every finish in this catalog. Corrosion is derived from salt-spray test duration and surface hardness from the finish layer's Vickers hardness where a measured figure exists; a finish that leaves the base metal's own surface is not rated for hardness. Cosmetic, lubricity and cost are FabDigit's engineering assessment. Scores and typical figures are screening data, not matched side-by-side tests or service-life rankings; ASTM B117 is a controlled salt-fog method, not a field-life prediction.
| Score | Type II anodize | Type I anodize |
|---|---|---|
| Corrosion resistance | 71 Very good | 71 Very good |
| Surface hardness / wear | 54 Fair | 49 Fair |
| Cosmetic quality | 88 Excellent | 28 Low |
| Lubricity | 18 Low | 18 Low |
| Cost | 24 $$ | 48 $$$ |
Key numbers
| Property | Type II anodize | Type I anodize |
|---|---|---|
| Thickness | 5–25 µm | 0.5–7.5 µm |
| Surface hardness | 200–400 HV | 150–300 HV |
| Salt-spray test duration | 336 h | 336 h |
| Max service temperature | 80 °C | 80 °C |
| Electrical | Insulating | Insulating |
| Colours | clear, black, red, blue, gold, custom dye | natural gray |
| Relative cost | Standard ($$) | Premium ($$$) |
| Added lead time | 3–5 working days | 5–10 working days |
| RoHS | Compliant | Conditional |
| Instant quote | Yes | On request |
Bold marks the side that is ahead on a row where more (or less, for cost and lead time) is better. Ranges are the typical specification window; the drawing call-out fixes the class.
Which materials take each finish
| Material family | Type II anodize | Type I anodize |
|---|---|---|
| Aluminum | Yes | Yes |
| DMLS / SLM | With care | With care |
Specifications and drawing call-outs
Type II anodize
- MIL-A-8625 — Anodic Coatings for Aluminum and Aluminum Alloys
- AMS 2471 — Anodic Treatment of Aluminum Alloys, Sulfuric Acid Process, Undyed Coating
- AMS 2472 — Anodic Treatment of Aluminum Alloys, Sulfuric Acid Process, Dyed Coatings
- ISO 7599 — Anodizing of Aluminium and Its Alloys — Method for Specifying Decorative and Protective Anodic Oxidation Coatings on Aluminium
ANODIZE PER MIL-A-8625 TYPE II CLASS 2, BLACK, 0.0005 IN THICK; MASK ALL THREADS AND ELECTRICAL CONTACTS
Type I anodize
- MIL-A-8625 — Anodic Coatings for Aluminum and Aluminum Alloys
CHROMIC ACID ANODIZE PER MIL-A-8625 TYPE IB CLASS 1, SEALED; MASK ELECTRICAL BONDING SURFACES
Type II anodize vs Type I anodize — frequently asked
What is the difference between Type II anodize and Type I anodize?
Anodizing Type II and Chromic Acid Anodizing Type I are both anodizing & conversion coatings finishes; type II anodize is the lower-cost option ($$). Type I anodize is the thinner coating (0.5–7.5 µm), so it disturbs tight fits less.
When should I use Type II anodize instead of Type I anodize?
Choose Type II anodize when decorative color and broader availability matter.
Is Type II anodize or Type I anodize cheaper?
Type II anodize is the lower-cost finish ($$ against $$$ for Type I anodize) among the finishes FabDigit quotes. Both are priced per part with a lot minimum; the exact figure appears on the instant quote once the part is uploaded.
Do Type II anodize and Type I anodize protect equally against corrosion?
On paper, yes: both are rated 336 h in neutral salt spray (ASTM B117 or the qualification hours of the governing specification). In service the difference comes from sealing, thickness class and the substrate alloy rather than from the choice between the two.