Phosphate coatings consist of crystalline, non-reflective, water insoluble metal phosphates that are very adherent to the base metal. They can be associated in three main categories:
ZINC PHOSPHATE
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Heavy zinc phosphate that has the ability to retain rust inhibiting oils, preservatives, or other specified finishes.
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MIL-DTL-16232, Type Z
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Lighter zinc phosphate has a smoother crystal structure and is normally not oiled as it is used as a base for paint.
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DOD-DTL-16232, Type Z
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TT-C-490, Various Types and Methods
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DOD-P-50002, Type Z
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MANGANESE PHOSPHATE
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Chosen for wear resistance and the ability to retain oils.
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DOD-DTL-16232, Type M
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DOD-P-50002, Type M
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IRON PHOSPHATE
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Utilized as a paint or powder coating base.
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There are numerous proprietary phosphate baths within each group that meet specific part requirements.
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