MIL-DTL-16232
Phosphate Coating, Heavy, Manganese or Zinc Base
Covers heavy manganese-phosphate and zinc-phosphate coatings applied to ferrous metals by immersion.
What MIL-DTL-16232 specifies
MIL-DTL-16232 controls heavy phosphate coatings by base chemistry and supplementary treatment. Type M is manganese phosphate and Type Z is zinc phosphate. Class 1 uses a supplementary preservative or coating stated by the purchaser; Class 2 uses the specified standard oil or corrosion preventive; Class 3 has no supplementary treatment; and Class 4 chemically converts the phosphate and may receive a specified dye or supplementary treatment. Coating weight is controlled by type and intended use in the specification, while corrosion performance depends strongly on the supplementary treatment. Drawings should state Type M or Z, Class 1 through 4, required preservative, any color, masking, and whether coating-weight or salt-spray verification is required.
MIL-DTL-16232 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Coating weight | Requirement / test |
|---|---|---|---|
Type M Class 1 | Manganese-phosphate base with a purchaser-specified supplementary preservative treatment or coating. | Heavy manganese-phosphate coating; applicable coating-weight requirement is selected by the controlled specification and order. | Coating weight, coverage, adhesion, and specified supplementary-treatment performance. |
Type M Class 2 | Manganese-phosphate base with specified lubricating oil or Grade 3 corrosion preventive. | Heavy manganese-phosphate coating. | At least 48 h salt spray without corrosion with the required supplementary treatment. |
Type M Class 3 | Manganese-phosphate base with no supplementary treatment. | Heavy manganese-phosphate coating. | Coating weight, coverage, adhesion, and visual quality; no oil-based corrosion requirement applies. |
Type M Class 4 | Chemically converted manganese-phosphate coating; may be dyed or supplementary-treated when specified. | Heavy manganese-phosphate coating. | At least 72 h salt spray without corrosion when supplementary treatment is applied. |
Type Z Class 1 | Zinc-phosphate base with a purchaser-specified supplementary preservative treatment or coating. | Heavy zinc-phosphate coating; applicable coating-weight requirement is selected by the controlled specification and order. | Coating weight, coverage, adhesion, and specified supplementary-treatment performance. |
Type Z Class 2 | Zinc-phosphate base with specified oil or Grade 3 corrosion preventive. | Heavy zinc-phosphate coating. | At least 72 h salt spray without corrosion with the required supplementary treatment. |
Type Z Class 3 | Zinc-phosphate base with no supplementary treatment. | Heavy zinc-phosphate coating. | Coating weight, coverage, adhesion, and visual quality; no oil-based corrosion requirement applies. |
Type Z Class 4 | Chemically converted zinc-phosphate coating; may be dyed or supplementary-treated when specified. | Heavy zinc-phosphate coating. | Specified class-system corrosion and supplementary-treatment tests. |
Tests and the drawing call-out
Tests the document imposes
- Coating weight by stripping and gravimetric measurement
- Visual coverage and crystal quality
- Adhesion and rub resistance
- ASTM B117 salt spray for supplementary-treated systems
- Hydrogen-embrittlement relief for susceptible high-strength steel
How to cite it
Drawing call-out
PHOSPHATE COAT PER MIL-DTL-16232 TYPE <M|Z>, CLASS <1|2|3|4>, [SUPPLEMENTARY TREATMENT], [COLOR], [MASKING]Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Finishes specified to MIL-DTL-16232
Manganese PhosphateBlack oxide & phosphateManganese phosphate is a heavy crystalline conversion coating for steel that retains oil and improves running-in behavior on loaded sliding parts.CorrosionHardnessCost$$
Zinc PhosphateBlack oxide & phosphateZinc phosphate forms a crystalline conversion layer on steel, principally as an adhesion and corrosion-resistance base for paint, powder coat, or oil.CorrosionHardnessCost$MIL-DTL-16232 — frequently asked
What is Type M versus Type Z?
Type M is manganese phosphate and Type Z is zinc phosphate. Manganese phosphate is commonly selected for wear and oil retention; zinc phosphate is commonly used for corrosion protection and paint preparation.
What do Classes 1 through 4 mean?
They identify the supplementary treatment: specified treatment for Class 1, standard oil or preservative for Class 2, none for Class 3, and chemical conversion for Class 4. They are not thickness grades.
Does Class 3 pass salt spray without oil?
Class 3 intentionally has no supplementary treatment and should not be assumed to provide the salt-spray performance of an oiled Class 2 system.
MIL-DTL-16232 is a work of the US Government and not subject to copyright. The authoritative copy is the DLA ASSIST database; check it for amendments issued after this page was updated. Official source ↗