Last updated on February 23rd, 2026 at 09:43 am
When it comes to protecting your metal parts, the choice of finish is crucial for both the functionality and aesthetics of the final product. At Approved Sheet Metal, we offer a variety of metal finishing options. Among these options, zinc plating stands out as a versatile and effective solution. In this post we will talk about what zinc plating is, common applications of zinc plating, and what type of zinc plating is right for your project.
Table of Contents
What is Zinc Plating?
Zinc plating is a process in which a thin layer of zinc is applied to the surface of a metal part. This is typically done through electroplating, where the metal part is submerged in a zinc-containing solution and an electric current is passed through, causing zinc to adhere to the part's surface.
The primary purpose of zinc plating is to provide corrosion resistance. Zinc acts as a sacrificial coating, corroding before the underlying metal does, thereby protecting it from rust and other forms of degradation.
In most industrial applications, zinc plating is specified under ASTM B633, which defines coating thickness, service conditions, and supplementary treatments such as chromate conversion coatings.
Zinc Plating Thickness and Industry Standards
Under ASTM B633, zinc plating thickness is typically specified based on service condition:
- SC1 (Mild): ~5 microns (0.0002")
- SC2 (Moderate): ~8 microns (0.0003")
- SC3 (Severe): ~13 microns (0.0005")
- SC4 (Very Severe): ~25 microns (0.001")
Thicker coatings generally provide increased corrosion resistance, often measured in salt spray testing hours. However, thicker zinc layers can affect tight tolerances, especially on threaded components or precision sheet metal parts.
Understanding the required service environment — indoor, outdoor, high humidity, marine exposure — helps determine the appropriate zinc thickness for long-term performance.
Applications of Zinc Plating
Zinc plating is commonly used in various industries, including automotive, aerospace, and construction, due to its cost-effectiveness and reliable performance. It is an excellent choice for parts that need to withstand harsh environments and maintain their integrity over time. Additionally, zinc plating can improve the appearance of metal parts, making them more attractive for customer-facing applications.
Zinc plating is often used with the following metals:
- Steel (Mild Steel/Carbon Steel): The most frequently zinc-plated sheet metal, steel benefits greatly from the corrosion resistance provided by zinc plating.
- Stainless Steel: While stainless steel is already corrosion-resistant, zinc plating may be used in specialized environments, though this is less common.
- Galvannealed Steel: A zinc-coated steel that has been heat-treated for improved paint adhesion.
- High-Strength Low-Alloy Steel (HSLA): Often used in structural applications. Zinc plating provides corrosion resistance while maintaining strength characteristics.
- Aluminum: Less common, but used in specific demanding environments.
- Copper and Brass: Typically plated to improve corrosion resistance or surface properties in electrical components.
Type I vs. Type II Zinc Plating
When considering zinc plating for your metal parts, it is important to understand the technical differences between Type I and Type II classifications.
In general:
- Type I refers to zinc plating without a chromate conversion coating.
- Type II includes a chromate conversion coating, typically clear/blue in appearance.
Type I Zinc Plating
Type I zinc plating provides sacrificial corrosion protection but does not include a supplementary chromate layer. The resulting finish is typically duller and may appear less uniform.
This option is commonly selected for internal components or parts where corrosion resistance is required but cosmetic appearance is not critical.
Type II Zinc Plating
Type II zinc plating includes a chromate conversion coating applied over the zinc layer. This creates the familiar blue-tinged or clear shiny finish and improves corrosion resistance performance.
The chromate layer enhances salt spray resistance and provides a more uniform, visually appealing finish. Type II zinc plating is far more commonly requested than Type I due to its improved appearance and performance.
Hydrogen Embrittlement Considerations
For high-strength steels — particularly HSLA or heat-treated fasteners — electroplating introduces the risk of hydrogen embrittlement. During the plating process, hydrogen can be absorbed into the metal, potentially leading to delayed cracking under stress.
To mitigate this risk, parts are typically baked after plating to relieve hydrogen. This step is especially important for structural components and load-bearing assemblies.
Cost and Lead Time Considerations
Zinc plating is one of the most cost-effective corrosion protection methods available, but several factors can influence pricing and turnaround time:
- Coating thickness: Thicker zinc deposits increase material usage and processing time.
- Part geometry: Complex shapes may require racking instead of barrel plating, increasing labor.
- Post-plating baking: Required for high-strength steels to prevent hydrogen embrittlement.
- Volume: Larger production runs benefit from plating efficiencies.
In many sheet metal applications, zinc plating adds minimal lead time compared to more complex finishing processes like powder coating or anodizing.
Choosing the Right Zinc Plating Option for Your Needs
Both Type I and Type II zinc plating provide sacrificial corrosion protection. At Approved Sheet Metal, we offer both Type I and Type II zinc plating for the same price, allowing you to select the option that best fits your project requirements.
If the part will be visible to end users, Type II zinc plating is typically the better option due to its clean and shiny finish. For internal components where appearance is not a concern, or parts where minimizing coating buildup is important for tight tolerances, Type I zinc plating may be appropriate.
When you provide us with details about the intended use, service environment, and performance expectations of your parts, we can help determine the correct thickness, service condition level, and plating type.
Choosing the right zinc plating from the start can save time, money, and ensure the longevity and appeal of your metal products. Reach out to us for expert advice and request a quote for high-quality zinc plating services tailored to your specific needs.
