Black oxide is a common coating typically applied to iron and steel. It is created by immersing the part in an oxide salt solution at approximately 285 degrees F. While mostly applied to iron and steels, it can be applied to nonferrous metals such as aluminum under suitable conditions. It cannot, however, be applied over plated parts (e.g. chrome, zinc, nickel, etc).
Black oxide on steel provides only marginal corrosion resistance. However, when applied to stainless steel or brass alloys, it will provide exceptional corrosion resistance even in harsh environments. Black oxide will not provide a smoothing effect like painting or painting. Any surface imperfections present in your substrate will still be present in your black oxide coated part.
A supplementary coating can be added after the black oxide process is performed. This coating, called an “after-finish”, will dictate the appearance and corrosion resistance of the coating. Without the after-finish, black oxide has poor corrosion resistance.
Advantages to black oxide coating include the following:
- No dimensional, physical or mechanical changes to material properties: black oxide changes the color of the surface metal – it does not add or remove any material from the metal
- Dark black color: can be a matte or shiny black depending on the surface finish of the substrate, and the type of after-finish applied
- Additional coating for increased protection: normal after-finishes are Oil, Wax, Lacquer, and Chromic Seals. These can improve the appearance, abrasion resistance, and corrosion resistance of the part
- Improved lubricity and anti-galling characteristics: an oil or wax after-finish is used to achieve these properties
- Weldable: black oxide does nothing to diminish a metals weldability, and does not produce noxious gases when welded
- Will not chip or rub off: must be removed mechanically by abrasion or chemically by etching
- Innexpensive: one of the least expensive methods of corrosion resistant or decorative coatings