Anodizing, conversion & passivation · finish comparison
Black Oxide vs Zinc Phosphate
Black Oxide and Zinc Phosphate are both black oxide & phosphate finishes; black oxide is the lower-cost option ($).
Black Oxide
Black oxide & phosphate · $ · instant quote
Black oxide converts the surface of ferrous parts to black magnetite for low-reflectance appearance and minimal dimensional change.
Zinc Phosphate
Black oxide & phosphate · $ · instant quote
Zinc phosphate forms a crystalline conversion layer on steel, principally as an adhesion and corrosion-resistance base for paint, powder coat, or oil.
When to choose which
Choose Black oxide
Choose Black oxide when minimal dimensional change is primary.
- Only about 0.5–2 µm thick
- Maintains thread and bearing-fit dimensions
- Produces nonreflective black appearance
Choose Zinc phosphate
Choose Zinc phosphate when the primary purpose is a paint base.
- Provides an anchored crystalline base for paint
- MIL-DTL-16232 classes control coating mass (commonly 11 g/m² minimum for Type Z)
- Improves underfilm corrosion resistance
What the numbers say
- Black oxide is the lower-cost option ($).
- Black oxide is the thinner coating (0.5–2 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 | Black oxide | Zinc phosphate |
|---|---|---|
| Corrosion resistance | 38 Fair | 38 Fair |
| Surface hardness / wear | — — | — — |
| Cosmetic quality | 55 Good | 18 Low |
| Lubricity | 30 Low | 38 Fair |
| Cost | 10 $ | 18 $ |
Key numbers
| Property | Black oxide | Zinc phosphate |
|---|---|---|
| Thickness | 0.5–2 µm | 2–15 µm |
| Salt-spray test duration | 24–72 h | 24–72 h |
| Max service temperature | 300 °C | — |
| Electrical | Semi-conductive | Semi-conductive |
| Colours | black | gray |
| Relative cost | Budget ($) | Budget ($) |
| Added lead time | 2–4 working days | 2–4 working days |
| RoHS | Compliant | Compliant |
| Instant quote | Yes | Yes |
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 | Black oxide | Zinc phosphate |
|---|---|---|
| Steel | Yes | Yes |
| DMLS / SLM | With care | With care |
| Stainless Steel | With care | No |
Specifications and drawing call-outs
Black oxide
- MIL-DTL-13924 — Coating, Inorganic, Black, for Ferrous Metals
BLACK OXIDE PER MIL-DTL-13924 CLASS 1, WITH WATER-DISPLACING PRESERVATIVE OIL; UNIFORM BLACK APPEARANCE
Zinc phosphate
- MIL-DTL-16232 — Phosphate Coating, Heavy, Manganese or Zinc Base
ZINC PHOSPHATE PER MIL-DTL-16232 TYPE Z, CLASS 1, 11 G/M² MINIMUM COATING WEIGHT; APPLY CORROSION-PREVENTIVE OIL
Black oxide vs Zinc phosphate — frequently asked
What is the difference between Black oxide and Zinc phosphate?
Black Oxide and Zinc Phosphate are both black oxide & phosphate finishes; black oxide is the lower-cost option ($). Black oxide is the thinner coating (0.5–2 µm), so it disturbs tight fits less.
When should I use Black oxide instead of Zinc phosphate?
Choose Black oxide when minimal dimensional change is primary. Conversely: choose Zinc phosphate when the primary purpose is a paint base.
Is Black oxide or Zinc phosphate cheaper?
Black oxide is the lower-cost finish ($ against $ for Zinc phosphate) 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 Black oxide and Zinc phosphate protect equally against corrosion?
On paper, yes: both are rated 24–72 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.