There are several surface treatments that have the potential to increase the durability of metal parts. Among the most widely used in the industrial sector are black oxide and galvanizing.
If you’re trying to decide between these two finishes for your parts or components, you’ve come to the right place!
In this article, our specialists will tell you everything you need to know about these two treatments. In the paragraphs that follow, you’ll find out which one is best for your project.
Black Oxide Definition
Black Oxide is defined as a chemical process used to treat the surface of metals to protect them from corrosion and improve their aesthetic appearance.
The process produces a surface layer of protective iron oxides on the metal, usually black or brown in color.
Metals Compatible with Black Oxide
Black oxide finishing is suitable for the following metals:
- Standard steel
- Low alloy steels
- Copper alloys
- Copper based alloys
- Wrought iron
- Cast Iron
- Malleable Iron
Examples of Black Oxide Treated Parts
Black Oxide treatment is commonly used to coat the surface of parts such as:
- Firearms
- Machine tools
- Mechanical parts
- Machined parts
- Screws, bolts, springs, etc.
The Black Oxide Treatment Process
Here’s how a black oxide part is typically treated:
- Degreasing: The surface of the part is cleaned to remove any grease, oil or dirt.
- Pretreatment: Some processes may involve pre-treatment, such as acid pickling, to remove any contaminants.
- Burnishing solution immersion: The part is immersed in a special chemical solution. This solution may contain compounds such as copper salts, selenium salts, or other chemicals.
- Chemical Reaction: The chemical reaction between the metal and the solution causes a protective oxide layer to form on the metal surface.
- Washing and drying: After the reaction, the part is washed to remove any residual chemical solution and then dried.
- Quality Control: The treated part is inspected to determine if the result meets standards.
Advantages and Disadvantages of Black Oxide
Advantages:
- No effect on part hardness
- Does not change the dimensions of treated parts
- Treated parts can be welded without producing harmful fumes
- Produces an easy-to-clean surface
- Can improve electrical conductivity
Disadvantages
- For superior corrosion protection, it must be combined with an oil or wax treatment.
You must work under ideal conditions to obtain consistent, high-quality results (variations in temperature, solution concentration and immersion time can have a significant effect).
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Galvanization Definition
Galvanizing is the process of coating metal with a thin layer of zinc to protect it from corrosion and extend its life. It takes its name from its inventor, the Italian Luigi Galvani (1737-1798).
Hot-dip or cold-dip galvanizing?
Hot-dip galvanizing involves immersing the part to be treated in a bath of molten zinc (at approximately 450 degrees Celsius), which chemically bonds to the metal surface. Hot-dip galvanizing generally produces a thicker layer of zinc than cold-dip galvanizing. This results in more robust corrosion protection and greater mechanical resistance.
In cold galvanizing, zinc is applied to the surface of the base metal at room temperature, often by immersion in a zinc solution or by electroplating. Cold galvanizing has a smoother appearance and brighter color than hot-dip galvanizing.
Metals Compatible with Galvanizing
The following ferrous metals can be galvanized:
- Iron
- Carbon steel
- Certain steel alloys
Examples of Commonly Galvanized Parts
Here are just a few examples of parts that are commonly galvanized:
- Fences, railings, guardrails and handrails
- Metal structures (beams, columns, supports, etc.)
- Steel pipes (ventilation and plumbing pipes, etc.)
- Automotive parts
- Agricultural equipment
- Marine and nautical equipment
- Window and door frames
Galvanizing Treatment Processes
- Surface preparation: The surface of the object is cleaned to remove grease, dirt and other impurities.
- Immersion in zinc bath: The object is immersed in a bath of molten zinc (hot-dip galvanizing) or a solution containing zinc compounds (cold-dip galvanizing).
- Formation of zinc layer: When the object is removed from the zinc bath, the zinc layer reacts with oxygen in the air to form an outer layer of zinc oxide.
- Quality Control: The galvanized part is inspected to ensure that the result meets standards.
Advantages and Disadvantages of Galvanizing
Advantages:
- Excellent corrosion protection (zinc acts as a sacrificial element that corrodes instead of the base metal)
- Galvanizing provides uniform protection on all surfaces of the item, including hard-to-reach areas.
- Galvanized items have a longer life due to their resistance to corrosion, making them suitable for harsh outdoor environments.
- The galvanizing process is relatively simple and can be applied to a wide variety of shapes and sizes of metal objects (sheets, beams, corners, etc.).
- Produces an easy-to-clean, low-maintenance surface.
Disadvantages:
- Galvanizing has a significant effect on the dimensions of the treated parts. The zinc layer is thick, making it unsuitable for machined or precision parts.
- Galvanizing often requires post-treatment as it closes bolt holes or small openings with mechanical functions.
- Galvanized steel is not easily painted.
- The protective zinc coating can be sensitive to acids, alkalis and chlorides.
- Under certain conditions (prolonged exposure to moisture), a white powdery substance called white rust may form on the surface. If this occurs, occasional cleaning and additional applications of protective coatings will be required to maintain corrosion resistance.
Choosing Between Black Oxide and Galvanizing: Factors to Consider
The choice between black oxide and galvanizing depends on several factors related to your specific needs. Here are some elements to consider:
- The level of corrosion protection required:
- Galvanizing provides excellent corrosion protection by forming a protective layer of zinc on the metal surface.
- Black oxidation, on the other hand, provides good corrosion protection when combined with an oil or wax treatment.
- Aesthetics:
- Black oxide produces a black or dark gray finish.
- Galvanizing gives a bright metallic appearance with a silver tint.
- Scratch and abrasion resistance:
- Galvanizing provides excellent scratch and abrasion resistance due to the hardened zinc layer.
- Black oxidizing may be slightly less scratch and abrasion resistant.
- Cost:
- Galvanizing can sometimes be more expensive due to the process involved.
- Black oxidizing can be more economical.
- Specific Applications:
- Galvanization is often used for parts that will be exposed to weathering or highly corrosive environments.
- Black oxide is often preferred for parts that will be used indoors.
- The metal to be treated:
- It’s important to determine which surface treatment is compatible with your type of metal.
- The size of the part to be treated:
- Galvanization can be used for large parts, while black oxidation is best suited for small or medium-sized parts.
For your black oxide needs, there’s Omnifab
In conclusion, if you’re wavering between black oxide and galvanizing, it’s important to have a good knowledge of each of these surface treatments to make an informed choice.
You can also seek expert advice. You can contact our team and they will give you a straight answer.
And if you decide to go with black oxidation and need a fast, professional black oxide coating service, we’ve got you covered!
