Guide to Black Oxide Coating: Process and Applications

Jack Lie CNC machining expert

Specialize in CNC Milling, CNC Turning, 3D Printing, Urethane Casting, and Sheet Metal Fabrication Services.


Black oxide coating is one of the common surface treatments that widely acts on various materials, especially metal. Thus, this article will comprehensively explain how black oxide coating works, its pros and cons, different types, and specific applications. Also, we will explore the wide range of materials suitable for black oxide coating as well as best practices.

What Is Black Oxide Coating?

Black oxide coating involves a thin black protective layer created on the workpiece surface by chemical reaction. Usually, this coating consists of a specially treated oxide layer, which is mainly employed for iron and its alloys, copper or brass. In addition to enhancing the corrosion resistance and wear resistance of metals, the coating also provides good lubricity and reduces light reflection. As a result, it greatly improves the overall performance and appearance of metal parts. Furthermore, this treatment method has an array of applications, from the automotive industries to the medical industries.

Black Oxide Parts

How does Black Oxide Work?

We now have a certain understanding of the definition of black oxide coating. Then, how does it work? The specific steps are as follows:

  1. Pre-treatment: First, manufacturers clean and pickle the metal surface to remove any dirt, grease, or oxides. This step ensures the smooth progress of the subsequent chemical reaction.
  2. Chemical Immersion: Next, the cleaned metal is immersed in a special reaction tank containing an alkaline solution. An oxidation reaction will occur on the metal surface to form a dense black oxide film at controlled temperature and time conditions.
  3. Post-treatment: After the immersion, workers will wash and dry the metal. Sometimes it requires further oil immersion or sealing treatment to enhance the corrosion resistance and wear resistance of the coating.

A series of complex chemical reactions will act on the metal surface and finally form a strong black oxide film. This coating is not only beautiful and elegant, but also effectively protects the metal from corrosion and wear.

Pros and Cons of Black Oxide Finish

Black oxide coating yields a host of benefits in practical applications. However, it also has some limitations, and below are its pros and cons.

Advantages:

  • Strong Corrosion Resistance: It can effectively prevent oxidation and corrosion of metal surfaces, greatly extending the service life of metal parts.
  • Good Wear Resistance: The coating surface is hard and dense, which can improve the wear resistance and abrasion resistance.
  • Good Lubrication Performance: It also has good self-lubrication, which can reduce friction and wear on metal surfaces.
  • Appearance: The coating can give metal parts an elegant black appearance and enhance the beauty of the product.
  • Cost-friendly: Black oxide treatment is simpler, faster, and more economical than other surface treatment processes.

Limitations:

  • Limited Coating Thickness: Black oxide finish is usually only a few microns thick and cannot provide too thick a protective layer.
  • Poor Heat Resistance: It is easy to fall off or oxidize in a high-temperature environment.
  • Easily Damage: During assembly or installation, the coating is susceptible to mechanical damage and wear.

Types Of Black Oxide Coating

There are mainly the following types of black oxide coatings

1. Traditional Black Oxide

This is the most basic and common type of black oxide coating. It refers to achieving a black oxide film by immersing the metal in a solution containing sodium hydroxide and sodium nitrite. This coating has good corrosion resistance and wear resistance, but poor heat resistance.

2. Hot Black Oxide

As its name suggests, hot black oxide coating is formed by chemical reaction at high temperature. Compared with traditional methods, this coating is denser and more heat-resistant, but with a higher cost.

3. Cold Black Oxide

This coating is a chemical reaction carried out at room temperature. The layer is relatively thin, but the processing process is simpler, faster, and less expensive.

4. Composite Black Oxide

This coating relies on the basic black oxide treatment and adds other chemical components such as polymers or metal particles. It can further improve the corrosion resistance, wear resistance, and heat resistance of the coating.

5. Electrochemical Black Oxide

It includes the use of electrochemical principles to form a black oxide film on the metal surface. This method can better control the thickness and uniformity of the coating.

Applications Of Black Oxide

Black oxide finish is extensively utilized in various industries, mainly including the following fields:

  • Mechanical manufacturing industry: Such as gears, bearings, screws and springs
  • Electronic and electrical industry: Including switches, connectors, and battery boxes
  • Automobile and aerospace industry: Engines, brake systems and landing gear
  • Military equipment field: Guns and missile launchers
  • Medical device industry: Involving surgical knives and orthopedic implants.
Black Oxide Coating

Materials Available for Black Oxide Coating

It’s an economical and practical surface finish and plays an important role in industrial production. Here are some common materials:

  • Aluminum and its alloys
  • Stainless steel
  • Copper and its alloys: Such as copper and brass
  • Carbon steel: Including ordinary carbon steel and alloy steel

Difference between Black Oxide And other Surface Finishes

Compared with other common surface treatment processes, black oxide coating has the following main contrasts:

CharacteristicBlack OxideOther Surface Finishes (e.g. Electroplating, Spraying)
FormationMechanismChemical reaction forms a dense oxide film on the metal surfaceDeposition or coating of other materials onto the surface
Coating ThicknessTypically 1-5 μmCan form thicker coatings
Wear ResistanceA wider range of colorsmore fragile
AppearanceUniform black finishWider range of colors
CostSimpler, faster, more economicalMore complex and resource-intensive

Best Practices for Black Oxide Coating

To ensure the quality and performance of black oxide coatings, it is necessary to pay attention to the following best practices:

  • Surface pre-treatment: Thoroughly clean and pickle the metal parts
  • Process parameter Control: Such as temperature, pH value, concentration,
  • Post-treatment: Water washing and drying
  • Inspection and Quality Control: Inspect the appearance, thickness, and adhesion
  • Environmental Protection: Appropriate deal with waste liquid
  • Process Optimization: Use heat treatment or composite coating to further improve the coating performance

Black Oxidation of your Metal Parts in Runsom

Runsom Precision is a company specializing in metal surface treatment, mainly providing various surface treatment services such as black oxidation, electroplating, and spraying. Moreover, Runsom has advanced production equipment and a strict quality management system. We customize various types of black oxidation coatings for customers to meet the needs of different industries and application scenarios. Please feel free to contact us if you want to customize your metal parts or ask for an instant quote.

FAQs

What does black oxide coating do?

Black oxide coating provides corrosion resistance, improved appearance, and reduced light reflection for metal parts.

What are the disadvantages of black oxide coating?

Black oxide coatings are relatively thin and can wear off over time with heavy use or abrasion.

Is black oxide better than zinc plated?

Black oxide and zinc plating serve different purposes. Black oxide provides a decorative finish, while zinc plating primarily offers corrosion protection. The choice depends on the specific application requirements.

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