Last updated on August 28th, 2026 at 09:46 am
Corrosion resistance starts long before a protective finish is applied. Material selection, environmental exposure, part geometry, drainage, joints, fasteners, welding, and finishing all affect how a sheet metal part performs over time.
Corrosion can affect much more than appearance. Depending on the application, it can cause pitting, loss of material, weakened joints, damaged finishes, poor electrical connections, or reduced service life.
It is not always possible to eliminate corrosion entirely, but engineers can significantly reduce corrosion risk by designing the part around its actual operating environment and selecting appropriate materials and finishes.
What Causes Sheet Metal Parts to Corrode?
Corrosion occurs when a metal reacts with its surrounding environment. The type and severity of corrosion depend on the material, moisture, temperature, chemicals, salts, surface condition, mating materials, and part geometry.
Several corrosion mechanisms are particularly relevant when designing fabricated sheet metal parts.
Uniform Corrosion
Uniform corrosion occurs relatively evenly across an exposed metal surface. Unprotected carbon steel exposed to moisture and oxygen is a common example.
Galvanic Corrosion
Galvanic corrosion can occur when dissimilar metals are electrically connected in the presence of an electrolyte such as water. One metal acts as the anode and corrodes more readily, while the other acts as the cathode.
This is important in sheet metal assemblies because the finished product may contain several different metals, including:
- Sheet material
- Self-clinching hardware
- Screws and bolts
- Hinges
- Brackets
- Washers
- Mating components
Material compatibility should therefore be considered across the entire assembly rather than evaluating the sheet material by itself.
Pitting Corrosion
Pitting is a localized form of corrosion that creates small cavities or pits in the metal surface. Certain stainless steels, for example, can be susceptible to pitting when exposed to chloride-containing environments.
Because pitting is localized, significant penetration can occur even when much of the surrounding surface still appears intact.
Crevice Corrosion
Crevice corrosion can develop in narrow gaps where moisture and contaminants become trapped. Overlapping sheet metal, bolted joints, seams, hardware interfaces, and other tight spaces can create these conditions.
Designing assemblies to drain, dry, or properly seal these areas can help reduce the risk.
Stress Corrosion Cracking
Some combinations of material, tensile stress, and corrosive environment can result in stress corrosion cracking. This is highly dependent on the alloy and service environment, so applications involving aggressive chemicals, chlorides, elevated temperatures, or other demanding conditions may require additional material engineering beyond standard fabrication DFM.
1. Design for the Actual Environment
The first step in designing a corrosion-resistant sheet metal part is understanding where and how the finished product will be used.
A component installed inside a climate-controlled electronics enclosure has very different corrosion requirements from a bracket exposed to road salt, outdoor humidity, condensation, cleaning chemicals, or a marine environment.
Before selecting material or finish, consider:
- Indoor or outdoor use
- Humidity and condensation
- Freshwater exposure
- Salt or chloride exposure
- Industrial chemicals or cleaning agents
- Operating temperature
- Expected service life
- Cosmetic requirements
- Electrical grounding or conductivity requirements
The more information your fabricator has about the application, the easier it is to identify manufacturing concerns before parts reach production.
2. Avoid Water Traps, Crevices, and Contaminant Buildup
Part geometry can have a major impact on corrosion resistance.
Whenever possible, design exposed sheet metal parts so moisture, dirt, salt, and other contaminants do not remain trapped against the material.
Potential problem areas include:
- Horizontal pockets that collect water
- Blind cavities that cannot drain
- Tight overlapping seams
- Areas around hardware that retain moisture
- Enclosed sections that cannot dry
- Recessed areas that are difficult to coat
Depending on the application, engineers may be able to improve drainage with strategically located drain holes, sloped surfaces, ventilation, more accessible seams, or different joint geometry.
Sealing may also be appropriate for some assemblies, but the sealing method and environmental requirements should be clearly defined by the customer.
3. Consider Galvanic Corrosion Between Dissimilar Metals
Choosing corrosion-resistant sheet material is only part of the design. Engineers also need to consider the other metals that contact it.
An aluminum enclosure, for example, may also contain stainless steel fasteners, self-clinching hardware, hinges, electrical components, and other mating materials.
When dissimilar metals are exposed to moisture or another electrolyte, galvanic corrosion may become a concern.
Depending on the application, potential mitigation strategies can include:
- Selecting more compatible material combinations
- Using appropriate coatings or surface treatments
- Electrically isolating dissimilar materials where appropriate
- Using insulating washers, bushings, or barriers
- Preventing moisture from collecting around the joint
- Selecting fastener and hardware materials with the environment in mind
If electrical grounding or bonding is required, however, electrically isolating the joint may not be an option. The corrosion requirements and electrical requirements need to be considered together.
4. Choose the Right Sheet Metal Material
Material selection plays a major role in corrosion resistance, but there is no single “non-corrosive” material that is ideal for every environment.
Common materials used for corrosion-resistant sheet metal applications include:
| Material | Corrosion Consideration |
|---|---|
| 5052-H32 Aluminum | Good general corrosion resistance combined with good formability, making it a common choice for formed aluminum parts. |
| 6061 Aluminum | Offers good corrosion resistance but is less ductile than 5052-H32 and typically requires larger bend radii when formed. |
| 304 Stainless Steel | Provides good general corrosion resistance for many indoor and outdoor applications. |
| 316 Stainless Steel | Provides improved resistance compared with 304 in many chloride-containing and more aggressive environments. |
| Carbon Steel | Economical and widely used, but typically requires a protective finish when corrosion resistance is important. |
| Galvanized Steel | Uses a zinc coating to provide barrier and sacrificial corrosion protection to the underlying steel. |
| Galvannealed Steel | Uses a zinc-iron coating and is commonly selected when corrosion protection and paintability are important. |
Learn more about stainless steel, sheet metal aluminum grades, and galvanized vs. galvannealed steel.
5. Account for Hardware, Fasteners, and Welded Joints
A corrosion-resistant assembly needs to be evaluated as a complete system.
Hardware and fasteners can introduce dissimilar metals, interrupt protective coatings, create crevices, or produce areas where moisture collects.
Welded assemblies introduce additional considerations. Weld seams, overlapping material, heat-affected surfaces, and enclosed geometry can affect both corrosion performance and the ability to apply a finish consistently.
If a welded assembly will be used in a corrosion-sensitive environment, identify the environmental exposure and required post-weld surface condition on the drawing or RFQ.
This is particularly important for assemblies where the appearance or corrosion resistance of the weld area is critical.
6. Select a Protective Finish for the Application
A surface finish can improve corrosion resistance, appearance, wear resistance, conductivity characteristics, or a combination of these properties.
The appropriate finish depends on the substrate material and application. Common options for fabricated sheet metal parts include:
- Powder coating
- Anodizing
- Chromate conversion coating
- Zinc plating
- Passivation
- Electroless nickel plating
- Electropolishing
- Tin plating
- Wet paint
When a project requires a particular industry or customer specification, clearly identify the specification, type, class, thickness, color, and any other required finish details on the drawing.
Do not select a finish based on corrosion resistance alone. Dimensional requirements, electrical conductivity, grounding, cosmetic appearance, wear, masking, hardware, and assembly requirements may also influence the choice.
Pre-Plated and Pre-Finished Material
Pre-coated or pre-plated sheet can reduce secondary processing, but fabrication can expose or disrupt protected surfaces.
Laser cutting or punching may expose cut edges, while forming and welding can affect the original coating in other areas.
Whether pre-finished stock or post-fabrication finishing is preferable depends on the material, geometry, required corrosion resistance, cosmetic requirements, and finish specification.
Powder Coating
Powder coating creates a polymer coating over the metal surface and can provide both corrosion protection and a durable cosmetic finish.
Corrosion performance depends on the complete coating system, including surface preparation, pretreatment, coating selection, coverage, and the environment in which the part will be used.
Powder coating is also electrically insulating. Grounding points, bonding surfaces, threaded connections, or other areas requiring metal-to-metal electrical contact may need to be masked.
Designers should also consider coating coverage around seams, edges, recessed geometry, welds, and hardware interfaces.
Anodizing
Anodizing creates a controlled oxide layer on aluminum that can improve corrosion resistance, wear characteristics, and appearance.
When specifying anodize, identify critical fits, threads, electrical contact areas, grounding points, and surfaces that require masking. Finishing requirements should be considered when establishing dimensional and assembly requirements.
Chromate Conversion Coating
Chromate conversion coatings are commonly used on aluminum to provide corrosion protection and prepare the surface for subsequent finishing.
When electrical conductivity or grounding is important, the exact coating specification and class should be defined by the application requirements.
Zinc Plating
Zinc plating is commonly used to improve the corrosion resistance of steel components. The zinc provides both a protective barrier and sacrificial protection for the underlying steel.
The required zinc type, thickness, color, and service condition should be identified on the drawing when they are important to the application.
Passivation
Passivation is commonly specified for stainless steel components to remove free iron contamination from the surface and support the material’s naturally occurring passive corrosion-resistant surface.
The required passivation specification should be identified on the drawing when applicable.
Wet Paint
Wet paint can provide a protective barrier and cosmetic finish for sheet metal parts. Like other barrier coatings, its effectiveness depends on surface preparation, coating coverage, application, and the service environment.
Scratches, chips, or other damage that exposes the underlying metal can reduce the protection provided by the coating.
Galvanized and Galvannealed Steel
Galvanized and galvannealed sheet use zinc-based coatings to help protect the underlying steel from corrosion.
The zinc provides barrier protection and can also provide sacrificial protection to exposed steel. Because fabrication operations such as cutting and welding can affect the coating, the complete manufacturing process should be considered when selecting pre-coated material.
7. Design for Finishing, Masking, and Electrical Contact
Finishing should be considered during design rather than added as an afterthought.
Clearly identify surfaces that must remain free of coating, especially when the part includes:
- Grounding points
- Electrical bonding surfaces
- Critical mating surfaces
- Threads
- Press-fit features
- Close-tolerance interfaces
- Cosmetic surfaces with specific appearance requirements
If the assembly depends on electrical continuity between components, specify those requirements clearly. A corrosion-resistant coating that electrically isolates two surfaces may create a problem if those same surfaces are supposed to provide a grounding path.
Corrosion-Resistant Sheet Metal Design Checklist
Before releasing a corrosion-sensitive sheet metal design, consider the following:
- Environment: Indoor, outdoor, humidity, condensation, salt, chemicals, or other exposure?
- Service life: How long is the part expected to remain in service?
- Material: Is the alloy appropriate for the environment?
- Drainage: Can water and contaminants escape?
- Crevices: Are there seams or pockets that can trap moisture?
- Hardware: Are fasteners, inserts, hinges, and other components compatible with the sheet material?
- Galvanic corrosion: Will dissimilar metals contact each other in a wet environment?
- Welds: Are post-weld appearance or corrosion requirements defined?
- Finish: Is the required finish and specification identified?
- Masking: Which areas must remain free of coating?
- Grounding: Are electrical contact and bonding surfaces clearly identified?
- Cosmetics: Are appearance requirements defined?
Talk to ASM About Your Corrosion Requirements
There is no single material or finish that provides the best corrosion resistance for every sheet metal application.
The right approach depends on the environment, material, geometry, hardware, welding, electrical requirements, finish, and expected service life.
When requesting a quote, provide Approved Sheet Metal with your 3D model and 2D fabrication drawing, along with the required material, finish specification, masking requirements, and any environmental or corrosion requirements that affect manufacturing.
Our team can review the design from a fabrication and DFM perspective and help identify material, forming, welding, hardware, and finishing considerations before the part reaches production.
