How to Choose the Right Surface Finish

The surface finish is often the last thing specified on a drawing, but it is one of the first things a customer sees and feels. The right finish protects against corrosion, improves appearance, and even affects how two mating parts fit together. At Suzhou Suhang Metal, we apply four common finishes to our CNC machined, stamped and extruded aluminum and steel parts: washing, anodizing, e-coating and powder coating. Learn more about our custom CNC machining services. Here is how to choose between the four finishes.

1. Washing (Cleaning & Passivation)

Washing is not a coating — it is a cleaning step that removes cutting oil, chips and oxide from the machined surface. It is the right choice when the part will be assembled, welded, anodized or coated in a later step, or when a bare, natural metal finish is all that is required.

• Best for: prototypes, parts that go into a further process, and internal components
• Pros: lowest cost, no dimensional change, keeps the raw metal look
• Cons: offers no corrosion protection or wear resistance on its own

2. Anodizing — Silver & Black

Anodizing is an electrochemical process that grows a hard, transparent oxide layer on aluminum. It is the standard finish for aluminum parts because it protects against corrosion and scratching while preserving a premium metallic look. The two most requested colors are natural silver and black.

• Silver (natural) anodizing: keeps the bright aluminum appearance, ideal for heatsinks, LED housings and cosmetic parts where you want the metal to show
• Black anodizing: a uniform, non-reflective black that hides fingerprints and machining marks — the go-to for amplifier chassis, audio enclosures and heat-dissipating components
• Pros: excellent corrosion and wear resistance, durable color, good heat dissipation
• Cons: only works on aluminum (and its alloys); adds a few microns of thickness that must be accounted for in tight-tolerance features

3. E-Coating (Electrophoresis)

E-coating, or electrophoretic coating, dips the part in a paint bath and uses an electric field to deposit a thin, uniform film. Because the current reaches into recesses and corners, it coats complex shapes evenly — something spraying and powder coating cannot always do.

• Best for: steel parts, complex geometries, and high-volume jobs that need consistent corrosion protection
• Pros: uniform thickness even inside holes and edges, strong anti-corrosion performance, low cost at volume
• Cons: limited color range (mostly black), thinner and less scratch-resistant than powder coating

4. Powder Coating (Spraying)

Powder coating electrostatically sprays a dry powder onto the part and then bakes it into a thick, tough skin. It is the most decorative and protective of the four, available in almost any color and texture.

• Best for: steel and aluminum enclosures, brackets and visible parts that need color, gloss or texture
• Pros: widest color range, excellent durability and outdoor resistance, hides surface defects
• Cons: thickest coating — not ideal for tight tolerances or threaded holes without masking; higher cost for small batches

How to Choose: A Quick Reference

Not sure which finish fits your part? Send your drawing to [email protected] and our engineers will recommend the most cost-effective option for your material, quantity and application.