I. What Is Galvanizing?
Galvanizing is the process of applying a layer of zinc to the surface of a metal. This zinc coating acts like a “rust-proof armor”, effectively isolating the substrate from air and moisture and preventing corrosion.
The bond between zinc and steel is more than a simple physical barrier; it also provides cathodic (chemical) protection. Even if the coating is slightly damaged, zinc will corrode preferentially, thus continuing to protect the underlying steel.
II. Main Types of Galvanizing
1. Hot-dip Galvanizing
Core principle: After surface preparation, steel parts are immersed in molten zinc at ~450 °C. An iron-zinc alloy layer forms through metallurgical reaction.
Key features: Thick coating, excellent corrosion resistance, long service life, full coverage (inside & outside). Too thick for tight-tolerance parts.
Appearance: Silver-grey, possible spangle pattern, slightly rough.
Typical uses: Power-transmission towers, highway guardrails, bridge steelwork, large pipes, building gratings.
2. Electro-galvanizing (Zinc Plating)
Core principle: In an electrolytic cell, zinc ions in solution are reduced and deposited on the part surface.
Key features: Uniform, bright, thin coating; high precision; little influence on dimensions or strength; can be color-passivated for decorative effect.
Appearance: Smooth & shiny—silver-white, blue-bright or iridescent after chromate.
Typical uses: Small automotive components, appliance housings, fasteners, household hardware, precision instruments.
3. Mechanical Galvanizing
Core principle: At room temperature, glass beads and zinc powder are tumbled with the parts, “cold-welding” zinc onto the surface by impact.
Key features: No hydrogen embrittlement, no thermal distortion, eco-friendly, low energy, good uniformity, adhesion slightly lower than hot-dip or electro.
Appearance: Matte grey, even but non-reflective.
Typical uses: High-strength bolts, springs, nails, washers and other parts sensitive to hydrogen embrittlement.
4. Sherardizing (Zinc Diffusion / Vapor Galvanizing)
Core principle: Steel parts are heated with zinc powder in a sealed rotating drum; zinc diffuses into the surface to form a zinc-iron alloy layer.
Key features: Alloy coating, high hardness & wear resistance, uniform thickness, no hydrogen embrittlement, process temperature lower than hot-dip.
Appearance: Dark grey, matte, uniform.
Typical uses: Complex-shaped small parts, fasteners, high-strength work-pieces, powder-metallurgy components.
5. Thermal Spray Zinc (Zinc Metallizing)
Core principle: A flame or electric arc melts zinc wire/powder, which is then atomized by compressed air and sprayed onto the surface.
Key features: No size limit, site-work possible, porous (usually sealed afterward), strong adhesion, flexible process.
Appearance: Grey-white, slightly grainy / coating-like.
Typical uses: Large steel structures—ship hulls, sluice gates, storage tanks, bridge cables, structural repairs.
III. How to Select the Right Process?
Maximum corrosion protection & long life → Choose hot-dip galvanizing.
High precision & decorative look → Choose electro-galvanizing.
High-strength steel, risk of hydrogen embrittlement → Consider mechanical galvanizing or sherardizing.
Oversized parts that cannot be dipped → Use thermal spray zinc.
IV. Closing Remarks
Though often seen as a common process, galvanizing is an indispensable protective technology in modern industry. It silently safeguards our infrastructure and greatly extends the service life of metal products.
With continuous industrial development, galvanizing technologies are also evolving:
- Environment-friendly processes are reducing pollutant emissions;
- Functional zinc coatings now provide extra properties—wear resistance, high-temperature durability, electrical conductivity—further expanding application fields.
Ningbo Qianhao Metal Products Co., Ltd. is a professional casting and machining manufacturer. We have established close partnerships with top-tier galvanizing plants to meet our customers’ surface treatment needs. We hope this article assists you in selecting the most suitable galvanizing option. Whether you are a new or long-standing partner, we are committed to serving you with full dedication and premium quality.
Author: Yanxiu Ji, Quality Manager
October 11, 2025