A Guide to Different Fastener Coatings and Finishes
The right coating or finish can make all the difference in determining how effective a fastener will perform over time, especially when exposed to various elements. Selecting fasteners with the proper coating for your application is critical for success. From zinc to black oxide to cadmium to phosphate and more, coatings can:
- Improve corrosion resistance
- Extend durability
- Enhance appearance
- Offer cost-effective solutions
The Importance of Fastener Coatings
Fastener coatings serve as more than just a polished finish. They’re a critical part of the overall integrity of a component or structure. A few ways fastener coatings and finishes help include:- Preventing rust and wear
- Reducing galling by minimizing friction
- Maintaining reliable mechanical performance
- Improving appearance for visible or decorative use
- Allowing use in various indoor and outdoor environments
Different Types of Fastener Coatings
Here is a detailed look at some of the most common fastener coating types.Zinc Coating
Zinc coatings are among the most popular fastener finishes and can be applied through electroplating or mechanical coating. They provide moderate corrosion resistance and are suitable for dry environments.Black Oxide
Black oxide coatings have a highly smooth surface, which reduces galling and wear between threads. This finish is applied in a highly thin layer that does not alter the fastener’s dimensions, and offers mild corrosion and abrasion resistance for indoor and outdoor environments.Hot-Dip Galvanized
Hot-dip galvanized fasteners (HDG) have been coated with a layer of zinc through a hot-dip process. This involves submerging a fastener in molten zinc to create a bond with the steel. This style of coating creates a thicker finish, which is ideal for extreme weather exposure and outdoor structures such as construction and building projects.Cadmium
Cadmium coatings offer excellent corrosion protection, particularly in marine environments. Although less common than other finishes due to environmental restrictions like RoHS, it is still widely used in marine, aerospace, and defense applications.Phosphate Coating
Phosphate coatings retain oil on their surface, making them excellent for reducing friction, improving lubricity, and increasing wear resistance. Popular for automotive and OEM manufacturing operations, phosphate-coated fasteners are a cost-effective alternative to cadmium finishes.Chrome and Nickel
Chrome and nickel fastener finishes are often chosen decorative finishes, as they provide a polished and aesthetic appearance. While they offer mild corrosion resistance, they are primarily chosen for their clean appearance and are used for automotive, architectural, and consumer applications.How to Choose the Right Fastener Coating
When determining which fastener coating is right for your application, consider:- The environment and conditions of your application
- The cost of different coatings
- Strength of fastener performance
- Galvanic compatibility with metals
- How the thickness of a coating affects thread fit