Black Oxide Finishing Coating Review
Mil-C-13924, Black Oxide Coating,
A black oxide finish offers a combination of properties that cannot be provided any other way. This conversion coating does not change the dimensional, physical or mechanical properties of the surface treated. The finish is inexpensive and easy to apply. It has an excellent appearance and is abrasion resistant. A uniform black coating for ferrous metals. Mostly a decorative coating. Only very limited corrosion protection under mild corrosion conditions.
Black oxide coatings should normally be given a supplementary treatment (i.e. oil displacement per Mil - C-16173 Grade 3 or protective treatments of Mil-C-16173).
No dimensional change effected. For moving parts which cannot tolerate the dimensional change of a more corrosion resistant finish. For decorative applications and may also be used to decrease light reflection.
Class 1 Alkaline Oxidizing. For wrought iron, cast and malleable irons, plain carbon, and low alloy steels. For corrosion resistance steel alloys which are tempered at 900F (482C) or higher.
Class 3 Fused salt oxidizing.
Class 4 Alkaline Oxidizing. For 300 series corrosion resistant steel alloys only.
Shall not be applied to aluminum alloys with over 5.0% copper, 7.0% silicon, or total alloying constituents over 7.5%. When copper content is less than 4.6% and for all suitable casting alloys be sure aluminum is tempered (such as -T4 or T6)