Selecting the appropriate protection for metal components is rarely a one-dimensional decision. Factors such as the environment, operating conditions, and expected service life play a decisive role in performance. Understanding how different solutions respond to corrosion is essential to choosing the most effective coating.
At Mercouris, we support industrial buyers with a broad technical portfolio that includes specialty lubricants, adhesives, sealants, resins, and silicones for industrial applications.
The real challenge is deciding which coating matches the type of failure that concerns you: rust during storage, salt exposure, galvanic corrosion, wear on sliding contacts, or aesthetic degradation? This guide will help you find the answer.
What is a metal coating?
A metal coating is a layer of metal (or a metal-containing layer) applied to a metallic substrate to protect it, extend its service life, or modify its surface performance. Coatings act as a barrier, while some provide cathodic (sacrificial) protection if the layer is damaged. Common application methods include hot-dip galvanizing, electroplating, cladding, thermal spraying, and vapor deposition.
Types of metal coatings
There is no universally “best” coating family. In practice, engineers group options based on their protection mechanism and application method.
Hot-dip Galvanizing (Zinc) for Steel
Achieved by immersing iron and steel in molten zinc, forming a durable protective layer.
- Why engineers choose it: Excellent long-term corrosion resistance for outdoor structures, good tolerance to minor damage due to zinc’s sacrificial action, standardized inspection practices according to ISO.
- Potential limitations: The increased thickness may affect tolerances on threads and mating surfaces.
Electroplated Coatings (Zinc, Nickel, etc.)
Used when a controlled, thin layer is required, mainly on fasteners and small components (e.g., according to ISO 2081).
- Advantages: Ideal for high-volume production, dimensional accuracy.
- Challenges: Risk of hydrogen embrittlement in high-strength steels, requiring controlled heat treatment.
Sherardising (Zinc Diffusion)
A zinc diffusion process ideal for complex shapes and internal surfaces, where uniform protection is required without the imperfections of hot-dip galvanizing.
Thermal Spray Coatings
Deposition of molten material onto large structures or for repair work. Allows the use of a wide range of materials (Zn, Al, alloys), but requires critical surface preparation.
Vapor Deposition (PVD/CVD)
Used when surface hardness and wear resistance are priorities (e.g., cutting tools), alongside corrosion protection.
Anodizing (for Aluminum)
A special case where the oxide layer of the metal itself is thickened to improve corrosion and wear resistance.
Anti-friction Coatings
Corrosion often begins where the coating wears due to friction. Molykote dry-film coatings create a lubricating film that covers surface roughness.
- Molykote 7400: Water-based dry-film lubricant for high loads and corrosion protection.
- Molykote D-321 R: Air-curing lubricant, ideal for sliding guides and permanent lubrication.
- Molykote 3402-C LF: Heat-curing coating designed to provide an excellent combination of lubrication and corrosion resistance.
Which coating is the best?
- For outdoor steel structures: Hot-dip galvanizing.
- For fasteners and precision components: Electroplated zinc (ISO 2081).
- For storage/transport protection: MOLYKOTE® Metal Protector Plus. A transparent wax-based coating that prevents rust during logistics without the need for a permanent finish.
- If friction causes corrosion: Anti-friction coatings that withstand mechanical stress.
Selection Checklist
- Define the exposure scenario (storage vs operation).
- Confirm the base material and any potential contact between dissimilar metals.
- Determine whether the coating is a “permanent finish” or “supply chain protection.”
- Align requirements with relevant standards (e.g., EN ISO 1461, ISO 9227 for salt spray testing).
- Define inspection criteria early (thickness, adhesion).
Protect your components, secure your operations. Contact us for technical support and to select the most suitable solution for your specific operating conditions.