Protecting Metallic Parts with Zinc Coating: A Guide to Electroplating and Galvanization
Zinc plated parts
Zinc is a highly corrosion-resistant metal with a shiny silver similar appearance. It can withstand harsh environmental conditions for an extended period without any degradation. Therefore, zinc is renowned as an excellent cover material in the surface finishing of metallic parts.
Applying the zinc coating layer on the surface of the substrate protects it from corrosion, abrasion, and wear. While it also provides an appealing aesthetic. Applying a zinc layer on the substrate material has several ways, such as electroplating, galvanization, spray painting, and sherardizing. However, zinc electroplating and galvanizations are the most popular method in the manufacturing industry.
This article will explore the zinc electroplating and galvanization processes with an in-depth comparison.
What is Zinc Plating or Electroplating?
Zinc electroplating is a popular surface finishing approach, which involves the electrochemical deposition of the zinc layer on the metal surface. It provides an inexpensive yet highly effective method of protecting metal objects from corrosion, making it an essential process for many industries.
The basic working principle of zinc electroplating involves the application of an electric current to the electrolyte solution. When an electric current passes through the electrolytic solution, it causes the zinc ions to dissolve and migrate toward the negatively charged metal substrate (part to be plated). As the zinc ions come into contact with the metal substrate, they are reduced and deposited onto the surface of the substrate in the form of a thin layer of zinc.
Let’s understand the working principle of zinc electroplating with the example of plating on steel parts.
At the anode (positive electrode):
Zn → Zn2+ + 2e-
At the cathode (negative electrode):
2H+ + 2e- → H2
Zn + 2H+ → Zn2+ + H2
In this process, zinc metal is oxidized at the anode, producing zinc ions in the solution. These zinc ions migrate towards the steel surface, where they are reduced at the cathode, forming a thin layer of zinc metal on the surface of the steel.
Which materials are compatible with a zinc electroplating finish?
Zinc electroplating can be used to finish the surface of several metallic substrates, including steel, iron, brass, copper, and aluminium. Nevertheless, not all materials are compatible since the parts need to be electrically conductive for any electroplating finish.
In addition, highly reactive materials with zinc are incompatible with zinc electroplatings, such as certain types of magnesium and titanium alloys.
Steps involved in the zinc electroplating process
The zinc plating process could be more complex than it sounds, especially if you are non-professional. It involves several steps, from surface preparation to post-processing of finished parts.
Zinc electroplating process
- Surface Preparation
Firstly, the substrate to be plated is cleaned and polished to remove any dirt, oil, or oxide layers on its surface. Then, substrates are immersed in a degreasing solution to remove any remaining oil or grease from its surface, followed by acid pickling and activation.
Only after surface preparation parts are immersed in a zinc ions plating solution a direct current is passed through the solution, which causes the zinc ions to be deposited onto the object’s surface.
After plating, the parts are washed and dried to remove any excess plating solution. The zinc coating is then passivized to improve its corrosion resistance.
The Galvanization Finish
Galvanization is a mechanical plating finish that involves coating a metal with a layer of zinc to protect it from corrosion. Zinc is a highly reactive metal that forms a protective barrier when it comes into contact with moisture, oxygen, or other corrosive substances. Galvanization can be performed on many metal substrates, including steel, iron, and aluminum.
The working principle of galvanization is based on the electrochemical reaction between the zinc and the metal substrate being coated. Zinc is a more reactive metal than steel, iron, or aluminum, which are commonly used as substrates for galvanization.
For example, the following electrochemical reaction occurs at the interface between the steel and the molten zinc during the galvanization of steel substrates.
Fe + Zn2+ → Fe2+ + Zn
The iron atoms on the steel surface substrate react with the zinc ions in the molten zinc bath to form ferrous ions and zinc atoms. The zinc atoms then diffuse into the surface and react with the iron atoms to form a layer of intermetallic compounds, creating a solid bond between the zinc coating and the steel substrate.
Steps involved in the galvanization process
Galvanization is done by immersing the substrate in a bath of molten zinc, which causes a coating on the substrate’s surface. The temperature of molten zinc ranges from 400 to 450 degrees Celsius.
There are several steps to accomplish the galvanization plating on the part’s surface.
- Surface Preparation
Firstly, the metal surface is cleaned to remove any dirt, corrosion, or other pollutants that could interfere with the bonding of the zinc coating. It is usually done with a wire brush or a degreasing solution. In addition, “pickling and fluxing” are carried out after cleaning to remove any remaining oxide or rust particles.
Once the surface preparation is finished, now parts are ready for galvanizing. It is dipped into a bath of molten zinc, which is typically held at a temperature of around 450 degrees Celsius. The zinc bonds to the surface of the metal and forms a protective coating. The duration of immersion in the molten zinc bath determines the thickness of the layer.
- Cooling and Finishing
After galvanizing, the metal is inspected to ensure the coating is even and consistent. The metal is then cooled and may be subjected to post-treatment processes such as quenching or passivation to improve the durability and performance of the coating.
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Advantages of Zinc Plating Finish
Zinc coating is a highly corrosion and abrasion-resistant finish that protects the underlying substrate for an extended period. It can be carried out in many ways, including electroplating and galvanization, and each method has unique benefits.
Firstly, let’s explore the typical advantages of zinc plating offered by both zinc electroplating & galvanization.
- Excellent corrosion resistance
One of the most significant advantages of zinc plating is its excellent corrosion resistance. The highly reactive nature of zinc metal allows the coating to readily react with atmospheric oxygen and water to form a barrier of zinc oxide layer on the surface. This barrier of oxide layer prevents the moisture and oxygen from reaching the underlying metal from corrosion.
Zinc is a widely available and reasonably inexpensive metal, making it an economical choice for surface treatment applications. So, it is a cost-effective method of protecting metal substrates from corrosion compared to other approaches, such as nickel or chromium plating.
Furthermore, zinc plating requires less maintenance than other protective coatings, which can assist in lowering long-term expenditures.
It is a versatile surface finish that can be applied to various metal substrates, including steel, iron, copper, and brass. Zinc plating can also create diverse surface finishes, including bright, matte, and black.
- Aesthetic Appeal
Zinc plating enhances the appearance of manufactured parts, making them more appealing to customers. Depending on the application, it can create a range of surface finishes, from a bright, shiny finish to a matte or black finish.
Distinctive Benefits of electroplating
- Electroplating allows for precise control over the thickness of the zinc coating. It is essential for applications where a specific level of protection is required.
- It maintains a highly uniform coating, which ensures that the entire surface of the substrate is protected from corrosion.
- Electroplating can develop zinc coatings of varying thicknesses, from thin decorative to thick industrial coatings.
Distinctive Benefits of galvanization
- It produces thicker zinc coatings than electroplating, making it an excellent alternative for applications requiring high corrosion protection.
- Galvanized coatings outlast other types of zinc coatings. It offers excellent resistance to abrasion, impact, and other mechanical wear.
- Galvanized coatings repair themselves. If the coating is scratched or damaged, the zinc reacts with moisture, generating a new zinc oxide layer.
What Are the Differences Between Zinc-electroplating and Galvanization?
Zinc-electroplating and galvanization are both effective methods for protecting metal from corrosion. However, there are many differences in complexity, coating thickness, cost, durability, applications, precision, process time, and other aspects.
Let’s overview the major differences through a comparison table.
|Complexity||Requires specialized equipment and expertise for the electroplating process.||A relatively more straightforward process involves dipping the metal into a bath of molten zinc.|
|Coating thickness||Generally thinner coating, typically between 5 and 25 microns.||Generally thicker coating, typically between 45 and 200 microns.|
|Cost||It can be more expensive due to the specialized equipment and labor involved in electroplating.||Generally more cost-effective due to the simplicity of the process.|
|Durability||It provides good corrosion resistance but may not be suitable for harsh environments or applications.||It provides excellent corrosion resistance and can withstand harsh environments or applications.|
|Applications||Used for small parts or components that require precision coatings, such as fasteners or electronic components.||Used for larger components, such as structural steel or fencing, and small parts.|
|Precision||Provides a more uniform and precise coating due to the electroplating process.||It can provide a less uniform and precise coating compared to electroplating.|
|Process Time||Typically requires longer process time compared to galvanization due to the electroplating process.||Generally requires less time due to the simplicity of the process.|
|Other||Can provide a more aesthetically pleasing finish due to the precision of the electroplating process.||Can result in a rougher or duller finish compared to electroplating.|
What Are the Applications of Zinc plating?
Zinc-plating is a versatile and effective process widely used to protect metal surfaces from corrosion in various industries and applications.
|Automotive||Brake components, engine parts, suspension components|
|Construction||Metal structures, pipes, beams, guardrails|
|Fastener||Screws, nuts, bolts, washers|
|Electronics||Connectors, heat sinks, circuit boards|
|Aerospace||Aircraft parts, engine components, landing gear|
Surface finishing is an essential step in manufacturing. It is responsible for protecting parts or products from corrosion and abrasion while providing an appealing appearance. Zinc plating is an effective and versatile surface finishing approach that can be applied in different ways to achieve the desired result.
Proleantech offer zinc plating and other surface finishing services at affordable price. We have several years of experience collaborating with various industries for quality surface finishing projects. So, contact us if you need surface finishing service for your current or upcoming project.
What is zinc- electroplating?
Zinc electroplating is a surface-finishing method that involves the electrochemical deposition of a thin zinc layer onto a metal substrate’s surface.
What is galvanization?
Galvanization is a mechanical plating finish that involves coating a metal with a layer of zinc to protect it from corrosion. Zinc is a highly reactive metal that forms a protective barrier when it comes into contact with moisture, oxygen, or other corrosive substances.
Which is a better finish, zinc electroplating or galvanization?
It depends on the application of part of the products. Electroplating offers precision, greater control over thickness, and highly uniform coating. On the other side, galvanization provides a thicker layer and costs less than electroplating.
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