Zinc Plating for Fasteners - How Much Do You Know
author: www.qishine.com
2026-03-01
We often hear about fastener zinc plating, but do you know how it's done? How many methods are there? Below, our company will introduce several commonly used zinc plating methods.
I. Electro galvanizing (Zinc Electroplating)
Electrogalvanizing, also known as cold galvanizing, is one of the most common surface treatment methods and process technologies in fastener manufacturing. It is a process that deposits a zinc layer onto a steel surface based on electrochemical principles. Unlike the metallurgical bond of hot-dip galvanizing, electrogalvanizing is a physical deposition process, resulting in a thinner, more uniform, and brighter coating. However, its corrosion resistance is relatively weaker. It is commonly used for parts requiring high dimensional accuracy, appearance, and conductivity. It looks good and is relatively inexpensive. The main color types include clear zinc (white), blue bright, blue-white, and yellow iridescent (chromate conversion coatings).
Electrogalvanizing, also known as cold galvanizing, is one of the most common surface treatment methods and process technologies in fastener manufacturing. It is a process that deposits a zinc layer onto a steel surface based on electrochemical principles. Unlike the metallurgical bond of hot-dip galvanizing, electrogalvanizing is a physical deposition process, resulting in a thinner, more uniform, and brighter coating. However, its corrosion resistance is relatively weaker. It is commonly used for parts requiring high dimensional accuracy, appearance, and conductivity. It looks good and is relatively inexpensive. The main color types include clear zinc (white), blue bright, blue-white, and yellow iridescent (chromate conversion coatings).
Simplified Process Flow:
Workpiece Loading → Mechanical Treatment → Unoil → Wash → Excitation → Enter the Plating Tank → Electro-Galvanized → Rinse out and Wash with Water → Passivation → Dry → Dehydrogenation → Unloading Finished Product
Workpiece Loading → Mechanical Treatment → Unoil → Wash → Excitation → Enter the Plating Tank → Electro-Galvanized → Rinse out and Wash with Water → Passivation → Dry → Dehydrogenation → Unloading Finished Product
Compared to other metal coatings, zinc is relatively inexpensive and easy to plate, but its corrosion resistance is average. Electrogalvanized coatings typically withstand neutral salt spray testing for up to 72 hours. Special sealants can extend this to over 200 hours, but the cost is significantly higher, about 5-8 times that of standard zinc plating.
During electrogalvanizing, fasteners treated with different plating solutions have their own advantages and disadvantages. Common plating solutions include: cyanide zinc plating, zincate zinc plating, chloride zinc plating, and sulfate zinc plating. The choice depends on specific requirements.
Performance Characteristics of Electrogalvanized Fasteners:
The zinc coating is relatively thick, with fine, uniform crystallization and no porosity, offering good corrosion resistance.
The electroplated zinc layer is pure, corroding slowly in acidic or alkaline atmospheres, effectively protecting the steel substrate.
After chromate passivation, the zinc coating forms white, colored, or olive drab finishes, which are aesthetically pleasing and decorative.
Due to its good ductility, the zinc coating can withstand cold stamping, rolling, bending, and other forming processes without damage.
As a surface treatment method, electrogalvanizing is low-cost, stable, reliable, and convenient.
The zinc coating is relatively thick, with fine, uniform crystallization and no porosity, offering good corrosion resistance.
The electroplated zinc layer is pure, corroding slowly in acidic or alkaline atmospheres, effectively protecting the steel substrate.
After chromate passivation, the zinc coating forms white, colored, or olive drab finishes, which are aesthetically pleasing and decorative.
Due to its good ductility, the zinc coating can withstand cold stamping, rolling, bending, and other forming processes without damage.
As a surface treatment method, electrogalvanizing is low-cost, stable, reliable, and convenient.
However, it is highly prone to hydrogen embrittlement, so dehydrogenation treatment should be performed promptly after plating. Additionally, it has poor acid/alkali resistance and relatively short corrosion protection life.
II. Hot-Dip Galvanizing
Hot-dip galvanizing involves immersing pre-treated fasteners into molten zinc to form a zinc and/or zinc-iron alloy coating on the surface, thus obtaining a metallic coating.
Hot-dip galvanizing involves immersing pre-treated fasteners into molten zinc to form a zinc and/or zinc-iron alloy coating on the surface, thus obtaining a metallic coating.
The coating thickness for hot-dip galvanized fasteners is typically 45–55 μm and is not easy to control precisely. However, it offers excellent corrosion resistance and is widely used in projects like steel tube towers, pole structures, angle steel towers, and photovoltaic power generation.
Simplified Process Flow:
Workpiece Loading → Degreasing → Rinsing → Pickling → Rinsing → Fluxing → (Drying) → Hot-Dip Galvanizing → Cooling → (Passivation) → Trimming/Inspection → Unloading Finished Product
Workpiece Loading → Degreasing → Rinsing → Pickling → Rinsing → Fluxing → (Drying) → Hot-Dip Galvanizing → Cooling → (Passivation) → Trimming/Inspection → Unloading Finished Product
Performance Advantages of Hot-Dip Galvanized Fasteners:
The service life of hot-dip galvanized workpieces is directly related to the coating weight (adhesion amount) besides the process itself. Other advantages include:
High Reliability: The zinc coating forms a metallurgical bond with the steel, becoming part of the steel surface, resulting in highly durable protection.
Complete Coverage: Every part of the workpiece is coated, including recesses, sharp corners, and hidden areas, providing comprehensive protection.
Low Processing Cost: The cost of hot-dip galvanizing for rust prevention is lower than other paint coatings.
The service life of hot-dip galvanized workpieces is directly related to the coating weight (adhesion amount) besides the process itself. Other advantages include:
High Reliability: The zinc coating forms a metallurgical bond with the steel, becoming part of the steel surface, resulting in highly durable protection.
Complete Coverage: Every part of the workpiece is coated, including recesses, sharp corners, and hidden areas, providing comprehensive protection.
Low Processing Cost: The cost of hot-dip galvanizing for rust prevention is lower than other paint coatings.
Time and Labor Saving: The galvanizing process for fasteners like bolts is more convenient and faster than other coating application methods. It also avoids the time and cost associated with on-site coating after installation. Furthermore, hot-dip galvanizing is a technology-based process, requiring less labor compared to labor-intensive protective coatings like sandblasting and painting.
Saving labor directly reduces expenses. Regarding time-saving, inspection is also simple and convenient. Hot-dip galvanized coatings can be inspected visually or with simple non-destructive coating thickness gauges.
Saving labor directly reduces expenses. Regarding time-saving, inspection is also simple and convenient. Hot-dip galvanized coatings can be inspected visually or with simple non-destructive coating thickness gauges.
The coating provides excellent protective capability, with better resistance to atmospheric corrosion than electrogalvanizing.
Disadvantage: Relatively lower environmental friendliness of the process.
Disadvantage: Relatively lower environmental friendliness of the process.
Qishine is ideal choice for EPC companies and project contractors.
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15960259563
III. Powder Sherardizing (Zinc Diffusion Coating)
The sherardized layer is formed by a zinc-iron diffusion reaction, primarily consisting of the δ phase (FeZn₁₇). This phase contains 7%–11% (mass fraction) iron, offers good density and toughness, and corrosion resistance not inferior to hot-dip galvanizing. Its hardness is around 250 HV, providing good wear resistance. The main component is pure zinc powder, mixed with appropriate fillers such as alumina, fireclay, and ammonium chloride.
The sherardized layer is formed by a zinc-iron diffusion reaction, primarily consisting of the δ phase (FeZn₁₇). This phase contains 7%–11% (mass fraction) iron, offers good density and toughness, and corrosion resistance not inferior to hot-dip galvanizing. Its hardness is around 250 HV, providing good wear resistance. The main component is pure zinc powder, mixed with appropriate fillers such as alumina, fireclay, and ammonium chloride.
Simplified Process Flow:
Workpiece Loading → Degreasing and Cleaning → Wash → Mechanical Rust Removal → Dedusting → Canning and Mixing → Heating diffusion → Cooling and separation → Aftercure → Unloading Finished Product
Workpiece Loading → Degreasing and Cleaning → Wash → Mechanical Rust Removal → Dedusting → Canning and Mixing → Heating diffusion → Cooling and separation → Aftercure → Unloading Finished Product
Characteristics of Powder Sherardizing:
The coating is uniform, does not cause hydrogen embrittlement or part distortion, making it particularly suitable for fasteners like nuts and bolts, small hardware, complex-shaped parts, and powder metallurgy products. Its disadvantages include poor working conditions, significant environmental pollution, and difficulty in automation.
The coating is uniform, does not cause hydrogen embrittlement or part distortion, making it particularly suitable for fasteners like nuts and bolts, small hardware, complex-shaped parts, and powder metallurgy products. Its disadvantages include poor working conditions, significant environmental pollution, and difficulty in automation.
IV. Mechanical Zinc Plating (Mechanically Deposited Zinc)
Mechanical zinc plating is a surface treatment process that forms a zinc coating on steel parts through the impact and collision of media (like glass beads) in the presence of zinc powder, dispersants, accelerators, and a liquid medium (usually water).
Mechanical zinc plating is a surface treatment process that forms a zinc coating on steel parts through the impact and collision of media (like glass beads) in the presence of zinc powder, dispersants, accelerators, and a liquid medium (usually water).
Simplified Process Flow:
Workpiece Loading → Deoiling and Degreasing → Wash → Deoxidation and activation process → Wash → Put into the Drum → Impact Medium and Activator → Pre-copper plating → Add zinc powder and deposition agent → Coating thickening and strengthening → Separation and discharge of waste liquid → Post-processing and Finishing → Unloading Finished Product
Workpiece Loading → Deoiling and Degreasing → Wash → Deoxidation and activation process → Wash → Put into the Drum → Impact Medium and Activator → Pre-copper plating → Add zinc powder and deposition agent → Coating thickening and strengthening → Separation and discharge of waste liquid → Post-processing and Finishing → Unloading Finished Product
This process is especially suitable for small fasteners, standard parts, and complex-shaped workpieces. It is favored for being hydrogen-embrittlement-free, low-energy, and environmentally friendly. The mechanical zinc plating layer is fundamentally different in process from electroplating and hot-dip galvanizing.
Characteristics of Mechanical Zinc Plating:
Process Feature: Operated at room temperature. The rotation of the plating barrel causes the impact media and parts inside to collide, generating mechanical impact force that deposits zinc powder onto the part surface, forming a coating with the basic physical characteristics of metallic zinc.
Process Feature: Operated at room temperature. The rotation of the plating barrel causes the impact media and parts inside to collide, generating mechanical impact force that deposits zinc powder onto the part surface, forming a coating with the basic physical characteristics of metallic zinc.
Process Characteristic: The mechanical plating process does not pose a hydrogen embrittlement risk to high-strength steels.
Process Defect: Coating thickness can be non-uniform; the coating is not as smooth or bright as electroplated coatings.
Process Defect: Coating thickness can be non-uniform; the coating is not as smooth or bright as electroplated coatings.
V. Dacromet (Zinc Flake Coating)
Dacromet is a transliteration and abbreviation of DACROMET. Domestically, it's named Zinc Chromate Coating. It is a new type of anti-corrosion coating primarily composed of zinc flakes, aluminum flakes, chromic acid, and deionized water.
Dacromet is a transliteration and abbreviation of DACROMET. Domestically, it's named Zinc Chromate Coating. It is a new type of anti-corrosion coating primarily composed of zinc flakes, aluminum flakes, chromic acid, and deionized water.
Simplified Process Flow:
Workpiece Loading → Degrease → Rust Removal → Machine Glzed Finish → Coating and curing → Aftercure → Unloading Finished Product
Workpiece Loading → Degrease → Rust Removal → Machine Glzed Finish → Coating and curing → Aftercure → Unloading Finished Product
Performance Characteristics of Dacromet:
Dacromet is a new surface treatment technology. Compared to traditional electroplating, Dacromet is considered a "green plating." Its advantages include:
Superior Corrosion Resistance: The Dacromet coating is only 4-8 μm thick, but its rust prevention effect is 7-10 times better than traditional zinc electroplating, hot-dip galvanizing, or paint coatings. Dacromet-treated standard parts and pipe fittings can withstand over 1200 hours of salt spray testing without red rust.
Dacromet is a new surface treatment technology. Compared to traditional electroplating, Dacromet is considered a "green plating." Its advantages include:
Superior Corrosion Resistance: The Dacromet coating is only 4-8 μm thick, but its rust prevention effect is 7-10 times better than traditional zinc electroplating, hot-dip galvanizing, or paint coatings. Dacromet-treated standard parts and pipe fittings can withstand over 1200 hours of salt spray testing without red rust.
No Hydrogen Embrittlement: The Dacromet process inherently avoids hydrogen embrittlement, making it highly suitable for coating stressed components.
High Heat Resistance: Dacromet can withstand high-temperature corrosion, with heat resistance up to 300°C. Traditional zinc plating starts to peel at around 100°C.
Good Adhesion and Recoating Performance: The Dacromet coating adheres well to metal substrates and bonds strongly with additional paint layers. Treated parts are easy to paint or color, with adhesion to organic coatings even surpassing that of phosphate coatings.
High Heat Resistance: Dacromet can withstand high-temperature corrosion, with heat resistance up to 300°C. Traditional zinc plating starts to peel at around 100°C.
Good Adhesion and Recoating Performance: The Dacromet coating adheres well to metal substrates and bonds strongly with additional paint layers. Treated parts are easy to paint or color, with adhesion to organic coatings even surpassing that of phosphate coatings.
Excellent Penetration: Due to the electrostatic shielding effect, it's difficult to electroplate zinc onto deep holes, narrow gaps, or the inner walls of tubes. Dacromet can penetrate these areas to form a protective coating.
Pollution and Hazard-Free: The entire Dacromet production, processing, and coating application process does not generate environmentally harmful wastewater or exhaust gases, eliminating the need for and cost of "three-waste" treatment.
Do you know what the thickness of the zinc coating on fasteners is
Fastener Zinc Plating vs PTFE Coating Comparison
Related Article
Insights from a Case Study on Exporting B8M Fasteners.Recently, during our final outgoing inspection of a batch of B8M stainless steel fasteners destined for Portugal, we discovered varying degrees of burrs on the edges of the bolt hex heads.
How to Efficiently Remove Burrs from Bolt Edges
Insulating Gasket Procurement Pitfalls: From "Price Traps" to "Supplier Selection"
What pitfalls should you watch out for when purchasing insulating gaskets
As a classic modified PTFE gasket material from Garlock, Gylon 3500 is widely used in petrochemical, chemical, and other industries for its excellent resistance to strong acids, solvents, and anti-creep properties.
How to Buy Genuine Gylon 3500 Insulating Gaskets at Competitive Prices in China
