Zinc plating is a surface treatment technology that forms a zinc coating on fasteners or other metal materials. Its purpose is to maintain an aesthetically pleasing appearance and provide long-term rust and corrosion resistance in complex environments such as air, moisture, and even acidic, alkaline, or saline conditions.
Zinc plating effectively extends the service life of bolts, nuts, screws, and other fasteners. Without protective treatment, steel fasteners are highly susceptible to corrosion and rust, potentially compromising engineering safety. In the fastener industry, the most common zinc plating methods are hot-dip zinc plating and electrogalvanizing. So, what exactly are they? And how do they differ? Let’s explore this in detail.
What Is Hot-Dip Galvanizing?
Hot-dip zinc plating, also known as hot-dip zinc coating, involves cleaning and derusting the surface of fasteners before immersing them in molten zinc at approximately 500°C. This process triggers complex physical and chemical reactions between the steel substrate and liquid zinc, forming a dense zinc alloy layer on the surface. The typical process sequence includes: Rust removal → Acid pickling → Water rinsing → Pre-treatment → Drying → Hot-dip zinc plating → Cooling → Passivation → Inspection.
Hot-Dip Galvanized Hex Bolts with Washers
Hot-dip Galvanized Flat Washers
What Is Cold Galvanizing
Cold zinc plating, also known as electrogalvanizing, deposits a uniform layer of zinc onto steel fasteners through an electrolytic reaction. The process flow includes: pretreatment → electrolytic plating → rinsing → passivation → drying → inspection. The entire process is completed at room temperature, hence the term “cold” zinc plating.
Self Tapping Screws with Blue Zinc Plated
Hex Flange Bolts with Color Zinc Plated
The Difference Between Hot- Dip and Cold Galvanizing
Hot-dip galvanizing is an electrochemical reaction. Cold galvanizing is a physical process.
Hot-dip galvanized surfaces lack the fine, bright finish of electrogalvanized ones, but the zinc coating thickness of hot-dip galvanizing is dozens of times greater than that of electrogalvanizing. Its corrosion resistance is also dozens of times greater than that of electrogalvanizing.
Hot-dip galvanized coatings are relatively thick, typically ranging from 30 to 150 μm. They offer superior corrosion resistance, strong adhesion, high hardness, and resistance to flaking. The surface exhibits a coarse texture with a silver-gray or dark gray appearance. It is suitable for long-term rust prevention on steel components exposed to outdoor environments with severe corrosion, such as highway guardrails, bridges, ships, power transmission towers, and large-sized fasteners—essentially, “rough” workpieces requiring durable protection.
Cold galvanizing produces a smooth, aesthetically pleasing, and flat surface on workpieces. However, due to the relatively thin coating—typically between 4 to 15 μm—its corrosion protection lasts for a shorter period. Cold galvanizing offers lower costs and faster processing speeds; yet its corrosion resistance is limited, making it suitable primarily for indoor or mildly corrosive environments. Applications include furniture, chassis bases, panels, mechanical components, and small fasteners.
| Item | Hot-dip galvanizing | Cold galvanizing |
|---|---|---|
| Product Process | Dip the fasteners into molten zinc at high temperature. | Electrolytically deposited zinc layer |
| Coating thickness | 30–150 μm | 4–15 μm |
| Adhesion | Strong, not easy to peel. | General, poor abrasion resistance. |
| Anti-corrosion life | 20–50 years | 1–5 years |
| Appearance | Rough, dark gray | Bright, beautiful, various colors |
| Cost | High | Low |
| Applicable Scenarios | Outdoor, heavily corrosive environments (bridges, seacoasts, railroads, electric utilities, large size fasteners) | Indoor or light corrosive environments (furniture, machine parts, small size fasteners) |
Where Can I Buy Galvanized Fasteners?
BD Fastener is a high quality galvanized fasteners supplier in China, providing hot-dip galvanized and cold-dip galvanized (yellow zinc, color zinc, white zinc, black zinc) fasteners products: hex bolts, nuts, screws, self-tapping screws, wood screws, self-drilling screws, washers and so on for global users. If you are looking for reliable fastener suppliers, please contact us.
- Materials: Carbon steel, stainless steel, alloy steel.
- Surface Treatment: Hot-dip galvanizing (zinc layer thickness 50-300ÎĽm), Dacromet coating, electro-galvanizing.
- Customization Service: Customization of special specifications, zinc layer thickness, and materials is supported.
- Quality Certifications: ISO 9001, IATF 16949 certified.
