Anodizing, conversion & passivation · finish comparison
Hard Anodizing Type III vs Plasma Electrolytic Oxidation
Hard Anodizing Type III and Plasma Electrolytic Oxidation are both anodizing & conversion coatings finishes; pEO is the harder surface (700–1,500 HV vs 350–550 HV).
Hard Anodizing Type III
Anodizing & conversion coatings · $$$ · instant quote
Type III hard anodizing forms a thick, dense aluminum-oxide layer for sliding, abrasive, and high-load service.
Plasma Electrolytic Oxidation
Anodizing & conversion coatings · $$$$
Plasma electrolytic oxidation, also called micro-arc oxidation, creates a thick ceramic oxide on aluminum or magnesium using high-voltage micro-discharges.
When to choose which
Choose Hard anodize
Choose Hard anodize when a standardized aluminum wear coating is adequate.
- Typical hardness is 350–550 HV
- Common 50 µm coating provides strong abrasive-wear resistance
- Sealed specimens are evaluated for 336 hours ASTM B117
Choose PEO
PEO is the pick when its strengths below matter more than Hard anodize's.
- Commercial systems span roughly 10–150 µm
- Local ceramic phases can measure about 700–2,000 HV
- Treats both aluminum and magnesium alloys
What the numbers say
- PEO is the harder surface (700–1,500 HV vs 350–550 HV).
- Hard anodize is the lower-cost option ($$$).
- Hard anodize is the thinner coating (25–75 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 | Hard anodize | PEO |
|---|---|---|
| Corrosion resistance | 71 Very good | 70 Very good |
| Surface hardness / wear | 61 Good | 74 Very good |
| Cosmetic quality | 50 Fair | 35 Fair |
| Lubricity | 25 Low | 20 Low |
| Cost | 44 $$$ | 78 $$$$ |
Key numbers
| Property | Hard anodize | PEO |
|---|---|---|
| Thickness | 25–75 µm | 10–150 µm |
| Surface hardness | 350–550 HV | 700–1,500 HV |
| Salt-spray test duration | 336 h | — |
| Max service temperature | 200 °C | — |
| Electrical | Insulating | Insulating |
| Colours | natural gray, black | white, gray, dark gray |
| Relative cost | Premium ($$$) | High ($$$$) |
| Added lead time | 4–7 working days | 7–15 working days |
| RoHS | Compliant | Conditional |
| Instant quote | Yes | On request |
Bold marks the side that is ahead on a row where more (or less, for cost and lead time) is better. Ranges are the typical specification window; the drawing call-out fixes the class.
Which materials take each finish
| Material family | Hard anodize | PEO |
|---|---|---|
| Aluminum | Yes | Yes |
| Magnesium Alloy | No | Yes |
| DMLS / SLM | With care | With care |
| Titanium | No | Limited |
| Zinc Alloy | No | Limited |
Specifications and drawing call-outs
Hard anodize
- MIL-A-8625 — Anodic Coatings for Aluminum and Aluminum Alloys
- AMS 2469 — Hard Anodic Coating on Aluminum and Aluminum Alloys
- ISO 10074 — Anodizing of Aluminium and Its Alloys — Specification for Hard Anodic Oxidation Coatings on Aluminium and Its Alloys
HARD ANODIZE PER MIL-A-8625 TYPE III CLASS 1, 0.0020 IN TOTAL COATING THICKNESS, UNSEALED; MASK THREADS AND BEARING FITS
PEO
No governing public specification — called out by name and thickness.
PLASMA ELECTROLYTIC OXIDATION PER APPROVED PROCESS SPECIFICATION FD-PEO-001, 50 ± 10 µm, SEALED, FINAL HARDNESS 900 HV0.05 MIN; MASK THREADS
Hard anodize vs PEO — frequently asked
What is the difference between Hard anodize and PEO?
Hard Anodizing Type III and Plasma Electrolytic Oxidation are both anodizing & conversion coatings finishes; pEO is the harder surface (700–1,500 HV vs 350–550 HV). Hard anodize is the lower-cost option ($$$). Hard anodize is the thinner coating (25–75 µm), so it disturbs tight fits less.
When should I use Hard anodize instead of PEO?
Choose Hard anodize when a standardized aluminum wear coating is adequate.
Is Hard anodize or PEO cheaper?
Hard anodize is the lower-cost finish ($$$ against $$$$ for PEO) 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.