Part manufacturers consider zinc plating more of a protective surface finishing process for metals like steel and iron. However, the electrochemical process is more than that, as it boasts a high aesthetic value due to the different types of zinc plating colors available.

The traditional zinc appearance after plating is grayish-blue or silver. However, different techniques can alter this color. As a result, this article will introduce zinc plating color techniques, achievable zinc colors, and possible applications.

Define Zinc Plating

Zinc plating or galvanization is the electrochemical or chemical deposition of a thin layer of zinc on a metal part. It is a protective surface finish treatment option that improves parts’ durability, corrosion resistance, and longevity.

Step-by-Step Guide to Zinc Plating

Zinc plating takes place using the following steps:

Cleaning

Cleaning the substrate (metal part) can be mechanical, electro-cleaning, or chemical. Physical and electrochemical cleaning will remove contaminants like dirt, grease, or rust, while chemical cleaning using acids will remove oxides on the substrate’s surface. 

Immersion or Electrolysis

On the one hand, in hot dip galvanizing, immerse the substrate in a molten zinc bath. On the other hand, in electrochemical zinc plating, immerse the substrate in a bath containing zinc salts (zinc sulfate or zinc chloride) and some additives. Afterwards, pass direct electric current through the bath which leads to the deposition of zinc on the substrate.

Post Treatment 

Post-treatment processes include chromate conversions, passivation, etc. They improve the zinc-plated part’s properties and aesthetic value.

Explain different types of zinc plating based on color

Zinc plating and its post-treatment process, such as chromate conversions, lead to different colors. Below is an overview of the different types of zinc passivation color techniques.

Zinc Plating Color Technique How it WorksZinc Color
Hot Dip GalvanizingThe zinc color technique involves immersing the substrate (mostly steel) in molten zinc at about 450°C (842°F). The zinc then bonds with the substrate.Traditional silver hue
Yellow Chromate CoatingThe post-treatment process involves immersing the zinc-plated part into a hexavalent chromium solution. This forms a thin chromate conversion coatingYellow
Trivalent Chromium ProcessThe zinc plating color technique involves depositing a trivalent chromium conversion coating on the zinc-plated surface.Iridescent (changes based on the angle)
Clear Zinc CoatingAn electrochemical process of depositing zinc on the substrate. The substrate is immersed in a zinc solution, and a direct electric current is passed. Blue tint
Colored Zinc Alloy CoatingElectrochemical or mechanical deposition of zinc alloys on the substrate  Variable
Zinc Plating Color Technique | How it Works | Zinc Color

Hot Dip Galvanizing

hot dipped galvanized part with gray zinc plating color
Hot dipped galvanized zinc part

Hot dip galvanizing is the mechanical deposition of zinc on a part (commonly steel alloy) by dipping it into a molten zinc solution. Consequently, the zinc coating bonds with the steel part, producing a silver or grayish-blue metal-zinc color. Functionally, the bond between both metals protects the steel from corrosion and makes it durable. 

Common Use and Applications

Hot dip galvanizing is the best zinc plating method for the non-tolerance part because it is difficult to control the coating thickness. Common industries and the parts made using the process are:

  • Construction: Beams, columns, and trusses used in bridges, highways, and buildings
  • Utilities: Electrical transmission towers, telecommunications poles, and water distribution systems.
  • Automotive: Chassis, frames, and body panels 
  • Agriculture: Fencing and livestock enclosures 
  • Infrastructure: Railings, guardrails, and highway barriers. 

Yellow Chromate Coating

Yellow chromate processed zinc part
Yellow chromate processed zinc part

Yellow chromate or zinc chromate coating is a post-treatment process for zinc-plated parts that involves electroplating the part. Immerse the zinc-plated part in a hexavalent chromium compound solution. Afterwards, pass a direct current through the bath to get a substrate with a bright yellow or gold-colored chromate conversion coating. 

The chromate coat protects the material from oxidation and rust. Furthermore, the color indicates corrosion resistance, and the part is corrosion-resistant as long as it persists.  

Common Use and Applications

Yellow chromate coating is the best option for parts that require short-term protection and a stringent gold zinc plating color without stringent requirements based on safety due to the environmental unfriendliness

Common industries and the parts made using the process are:

  • Automotive: Fasteners and brackets 
  • Hardware: Bolts, nuts, and screws 
  • Consumers’ goods: Appliances, furniture, and recreational equipment

Trivalent Chromium Process

trivalent chromate processed zinc part
Trivalent chromate processed zinc part

Trivalent chromium coating is another zinc plating color technique that involves electroplating. Immerse the part in a bath solution containing trivalent chromium compounds. Afterwards, passing direct current through the solution will deposit a greenish-yellow layer coat on the part. 

The coating protects the material from oxidation and rust. Furthermore, the trivalent chromate coat indicates the parts’ corrosion resistance. As long as the color persists, the part is corrosion-resistant. It also serves an aesthetic function. 

Environmental and Health Benefits

The zinc plating color technique is an alternative to the traditional hexavalent chromium plating method (yellow chromate coating). It does not use hexavalent compounds, which are carcinogenic and toxic. Consequently, it is more environmentally friendly. 

Common Use and Applications

Trivalent chromium plating is applicable in several industries due to its better environmental impact. They include:

  • Automotive: Trim, emblems, and decorative components
  • Consumer Goods: Faucets, fixtures, and other household appliances 
  • Hardware: Fasteners, fittings, and other hardware items

Clear Zinc Coating

clear zinc plating color
Clear zinc-coated part

Clear zinc coating is the electrochemical deposition of a thin layer of zinc on substrate metals. Clean the substrate using mechanical, chemical, and electrochemical means. Afterwards, immersed it in a bath containing only zinc salts. 

Pass a direct electric current through the bath to deposit the layer of zinc on the substrate. This technique produces a transparent hue for the zinc plating color, allowing the natural color and texture of the substrate to show. 

Moreover, clear zinc coating uses only zinc ions (without other additives such as chromates). As a result, this reduces the part’s corrosion resistance and its use in harsh environments compared to the other methods. 

Common Use and Applications

Clear zinc coating is often used in indoor or controlled environments where the corrosion resistance requirement is moderate. The zinc color coating technique is applicable in the following industries: 

  • Hardware and Fasteners: Bolts, nuts, screws, and other hardware parts
  • Automotive Components: Brackets, hinges, and clips 
  • Electronics: Electronic enclosures, connectors, and other components 
  • Consumer Goods: Furniture, appliances, and fixtures 
  • Architectural Applications: Hardware, signage, and decorative elements 

Colored Zinc Alloy Coatings

Colored Zinc Alloy Coatings
Colored Zinc Alloy Coatings

Colored zinc alloy coating is similar to clear zinc coating, although it adds other elements like aluminum or nickel. Cleaning the substrate. Afterwards, immerse it in the bath containing zinc and a controlled amount of aluminum and nickel salts. 

Passing a direct electric current through the bath deposits a thin zinc, aluminum, and nickel layer on the substrate. Depending on the type and concentration of the additives, you can have a wide range of zinc plating colors. 

Below is a list of metals and their color

AdditivesZinc Coating Color
AluminumBluish
NickelYellow, Gold, Bronze
IronDarker color
CobaltBluish or Grayish
CopperRed or Bronze
TinWhite

Due to the different metals, these distinctive zinc plating colors make them appealing aesthetically. As a result, they are suitable for both decorative and functional applications. Furthermore, the parts have better corrosion resistance than clear zinc coating and hot dip galvanization.

Common Use and Applications

Application of colored zinc alloy coatings include:

  • Automotive: Colored Trim, emblems, and decorative accents 
  • Consumer Goods: Furniture, fixtures, and household appliances 
  • Hardware and Fasteners: Bolts, nuts, screws, and other hardware items
  • Architectural Applications: Signage and building facade
  • Electronics: Enclosures and connectors

The Science Behind Zinc Plating Colors

Depending on the passivation technique, coating thickness, and additives, zinc plating can have different colors. Its colors range from silver to yellow, black, blue, or green. 

The Role of Chromates

Chromates can change color because they contain a transition metal (chromium) with variable oxidation states. Each oxidation state contributes uniquely to the zinc plating color. For example, hexavalent chromium compounds have a different color from trivalent ones. 

The color of the chromate also depends on the coating thickness and the electrolyte concentration. Thick chromate coatings are more vibrant, with thinner coatings appearing lighter.

Influence of Plating Thickness

The thickness of the zinc plating layer will affect the color. Thick coating layers will appear brighter than thin coatings. Additionally, the denser the coating, the tendency of uneven coating chromate thickness and uneven color distribution.

Impact of Post-Treatment Processes on Zinc Plating Colors

Post-treatment processes in zinc plating include chromate conversion coating, passivation, or sealing, and they have the following impacts on zinc-plated parts:

Corrosion Resistance

The post-treatment process is an additional barrier between the already zinc-plated parts and the environment. Consequently, it acts as an additional corrosion protection. 

Color Enhancement

Chromate conversion coatings can improve the color of zinc-plated parts. As a result, part manufacturers access yellow, black, and iridescent colors.

Adhesion Promotion

Chromate conversion coatings can improve the adhesion of paints and powder coatings to a zinc-plated surface.

Surface Conditioning

Post-treatment processes like passivation can improve the part’s surface finish by making it smoother and more uniform.

Common Zinc Plating Colors and Their Characteristics

Common colors associated with zinc plating and other techniques include: 

  • Bright Silver achieved with a hot dip zinc plating
  • Yellow or Gold achieved by chromate conversion coatings containing hexavalent chromium compounds 
  • Black is achieved using post-treatment processes that involve additives such as selenium or sulphur.
  • Blue or Green is achieved using additives like aluminum or nickel. 

ZINTILON Support for Zinc Plating Colors

The best way to ensure quality zinc coating on a part is to consider a reputable surface finishing service provider At Zintilon, aside from our state-of-the-art manufacturing capability, which provides quality parts. 

We offer quality-focused surface finishing options at competitive prices. Contact us for our fast lead time and competitive market pricing.

Conclusion

Part manufacturers consider zinc plating more of a protective process than an aesthetic one. In addition to the traditional silver hue, other zinc plating techniques and post-treatment methods can also alter the color of the end product. 

This article introduced zinc plating techniques and their respective colors. If you want a surface finishing treatment option for your zinc part, contact Zintillon.

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