Last updated on September 3rd, 2026 at 09:55 am
Metal finishing is an important part of custom sheet metal fabrication because the finish can affect corrosion resistance, wear resistance, electrical properties, appearance, and how the finished part fits or functions within an assembly.
At Approved Sheet Metal, finishing options include anodizing, chromate conversion coating, and powder coating. These processes serve different purposes, so the right choice depends on the base material and what the finished part needs to do.
Anodizing vs. Chromate vs. Powder Coating
- Anodizing is an electrochemical process that converts the surface of aluminum into a controlled aluminum oxide layer. It can improve corrosion and wear resistance while providing a clear or colored appearance. The anodized surface is also electrically resistive, which may require masking where electrical contact or grounding is needed.
- Chromate conversion coating is a thin chemical conversion treatment commonly used on aluminum to improve corrosion resistance while maintaining better electrical conductivity than anodizing or powder coating. This can make chromate useful for applications involving electrical bonding, grounding, or contact surfaces.
- Powder coating applies a dry coating electrostatically to the metal surface and then cures it to create a durable protective and decorative finish. Many industrial powder coatings use thermosetting formulations and are available in a broad range of colors, gloss levels, and textures.
Quick Finish Selection Guide
| If Your Priority Is... | Consider |
|---|---|
| Aluminum corrosion protection with a decorative finish | Type II anodize |
| Increased wear resistance on aluminum | Type III hardcoat anodize |
| Aluminum corrosion protection with electrical contact or bonding requirements | Chromate conversion coating |
| Broad color, texture, and gloss options | Powder coating |
| Very thin conversion coating | Chromate conversion coating |
| Electrical contact areas on an otherwise coated part | Chromate conversion or specified masking, depending on the application |
| Durable decorative coating across a variety of compatible metals | Powder coating |
This table is a starting point rather than a universal specification. The appropriate finish depends on the material, environment, dimensional requirements, electrical requirements, appearance, applicable specifications, and end use.
What Is Anodizing?
Anodizing is used on aluminum to create a controlled oxide layer that becomes part of the aluminum surface rather than a separate coating applied on top of it.
Two common categories engineers may encounter are Type II and Type III anodizing.
Type II Anodizing
Type II sulfuric anodizing is commonly used when a part requires corrosion protection along with a clear or decorative colored appearance. It is frequently specified for aluminum enclosures, covers, brackets, panels, and other fabricated components.
Type III Hardcoat Anodizing
Type III hardcoat anodizing creates a harder, more wear-resistant oxide layer and is generally selected when abrasion or wear performance is more important.
Because Type III anodizing has greater dimensional implications than a thin conversion coating, engineers should pay particular attention to critical holes, mating surfaces, threads, and other features where the finished dimensions matter.
Rather than simply calling out "black anodize," drawings should identify the required anodize type, class, color, and applicable specification when those requirements are important.
What Is Chromate Conversion Coating?
Chromate conversion coating creates a very thin conversion layer on the aluminum surface. It can provide corrosion protection while retaining better electrical conductivity than anodizing or powder coating.
That combination makes chromate useful for applications where electrical bonding, grounding, or conductive contact surfaces are required.
Chromate conversion coating may also be used as part of a specified finishing system or as a pretreatment before another coating. The exact process and specification should be identified when the application requires a particular performance level.
What Is Powder Coating?
Powder coating is applied to the surface of a metal part and cured to form a protective and decorative coating.
One of its biggest advantages is the range of available colors, gloss levels, textures, and formulations. Powder coating is commonly used on enclosures, panels, covers, brackets, chassis, and fabricated assemblies where appearance and surface protection are important.
Unlike anodizing and chromate conversion coating, powder coating is not limited to aluminum and can be used on a variety of compatible metal substrates.
Powder coating also creates more surface buildup than thin conversion finishes, so coating thickness needs to be considered anywhere fit, clearance, electrical contact, or assembly is critical.
Functional Comparison of Sheet Metal Finishes
| Consideration | Anodize | Chromate Conversion | Powder Coating |
|---|---|---|---|
| Common Substrate | Aluminum | Aluminum | Various compatible metals |
| Corrosion Protection | Yes | Yes | Yes |
| Wear Resistance | Can be good, particularly with Type III hardcoat | Limited compared with anodize or powder coat | Generally good, depending on coating system |
| Electrical Contact | Generally resistive | Better suited to conductive contact and bonding applications | Generally insulating |
| Color Options | Clear and dyed colors available | Limited appearance options | Broad color, gloss, and texture selection |
| Dimensional Considerations | Must be considered, especially with hardcoat | Very thin conversion layer | More significant coating buildup |
| Masking May Be Required | Yes | Yes | Yes |
| Common Reason for Selection | Corrosion, wear, and appearance on aluminum | Corrosion protection with electrical conductivity | Durable protective and decorative coating |
How Finishing Affects Dimensions and Assembly
The finish should be considered while the part is being designed, not after fabrication is complete.
Depending on the process and application, finishing can affect:
- Hole and slot dimensions
- Mating surfaces
- Press fits and close-clearance features
- Threaded features
- Self-clinching hardware
- Grounding and electrical contact points
- Gasket and sealing surfaces
- Assembly clearances
- Cosmetic surfaces
That does not mean engineers should automatically enlarge every hole or manually compensate every dimension for the expected finish thickness.
Instead, define the required finished-part dimensions and tolerances on the drawing and identify surfaces that have special functional requirements. The fabricator and finishing supplier can then determine whether masking, process allowances, or geometry changes are appropriate.
Masking Critical Areas Before Finishing
Some areas of a sheet metal part may need to remain free of anodize, chromate, powder coat, or a particular portion of the finishing process.
Depending on the design, masking may be required for:
- Threads
- Grounding points
- Electrical contacts
- Mating surfaces
- Bearing or locating surfaces
- Critical holes
- Gasket or sealing surfaces
- Specific cosmetic boundaries
Masking requirements should be identified clearly on the drawing rather than left for the fabricator or finisher to assume.
Choosing a Finish Based on Function
Consider Type II anodizing when:
- The part is aluminum
- Corrosion protection is required
- A clear or decorative anodized appearance is desired
- An anodized surface is specified for the application
Consider Type III hardcoat anodizing when:
- The part is aluminum
- Wear or abrasion resistance is an important requirement
- A harder anodized surface is required
- The design can accommodate the dimensional effects of the specified finish
Consider chromate conversion coating when:
- The part is aluminum
- Corrosion protection is required
- Electrical bonding, grounding, or conductive contact is important
- A very thin conversion coating is preferred
- The drawing or customer specification requires a particular conversion coating
Consider powder coating when:
- A broad range of colors is desired
- Gloss or texture is part of the cosmetic requirement
- A durable decorative coating is needed
- The coating buildup can be accommodated
- The part material is compatible with the specified powder coating process
Lead time should not be the only reason for selecting one finishing process over another. Availability can vary based on the finish specification, color, quantity, masking requirements, approved supplier requirements, certifications, and the finishing supplier's production schedule.
Wet paint is another valid finishing option for many applications. This article focuses on anodizing, chromate conversion coating, and powder coating because they are common finishing choices for the custom sheet metal parts Approved Sheet Metal supplies.
6 Tips for Designing Powder Coated Sheet Metal Parts
POWDER COATING
With over two decades of experience in powder coating, we’ve learned that a little bit of foresight yields superior outcomes. Here are our top tips for powder coated sheet metal parts.
A Quick Word on Color Matching
Color requirements should be communicated as specifically as possible, but the method depends on the finishing process.
RAL colors are commonly used to communicate powder coating and paint colors. In addition to the color, engineers may need to specify the required gloss, texture, powder manufacturer or product, or other cosmetic requirements when consistency is important.
A RAL number does not guarantee an exact visual match across different finishing processes. An anodized aluminum part should not be expected to exactly match a powder-coated part simply because a similar color is requested.
Anodized color can vary based on the aluminum alloy, surface condition, anodizing process, oxide layer, dye, sealing process, and normal lot-to-lot processing variation.
For applications where appearance or color matching is critical, consider establishing an approved sample, color coupon, or other visual acceptance standard before production.
What to Specify on Your Drawing
To help your fabricator quote and manufacture the finished part correctly, identify the finishing requirements as early as possible.
Depending on the project, the drawing or applicable specification should identify:
- Finish type
- Applicable finish specification
- Anodize type and class, when required
- Powder coat color
- Gloss or texture requirements
- Masking requirements
- Grounding or electrical contact areas
- Surfaces that must remain free of coating
- Cosmetic surfaces
- Critical finished dimensions
- Approved finish sample or color standard, when required
The more clearly these requirements are defined at the RFQ stage, the easier it is to account for finishing during fabrication, assembly, inspection, pricing, and lead-time planning.
Need finishing for your custom sheet metal parts? Request a quote and send us your 3D CAD model, drawing, quantity, and finishing requirements.
