Surface finishes are not just cosmetic. They influence corrosion resistance, electrical conductivity, hardness, and how the part feels in hand. The wrong finish can turn a structurally fine part into a warranty problem within months.
Anodize: the aluminum default
Anodizing creates a controlled aluminum oxide layer integral to the substrate. It does not chip or peel. Type II is the cosmetic default; Type III hardcoat doubles the layer thickness and approaches HRC 60 for wear resistance.
| Type | Layer thickness | Color options | Typical use |
|---|---|---|---|
| Type II clear | 5-25 µm | Clear or dyed | Aesthetic, mild corrosion |
| Type II black | 10-25 µm | Solid black | Consumer electronics |
| Type II color | 10-25 µm | Most RAL/Pantone | Branded products |
| Type III hardcoat | 25-100 µm | Bronze/gray | Wear-critical aluminum |
Powder coat for steel
Powder coat is the workhorse finish for steel and zinc-plated parts. The coating is electrostatically applied and cured around 200 °C, producing a 60-100 µm layer that resists salt spray for thousands of hours when applied over zinc.
- Use a primer (zinc plate or e-coat) under powder for outdoor or marine use.
- Match colors via RAL codes; Pantone matches require a sample run.
- Mask threads, datum surfaces, and electrical contact areas before powder.
- Glossy, matte, and textured finishes all available — call out gloss level.
Electroplating and conversion coatings
Plating adds a metallic layer with specific properties: zinc for sacrificial corrosion, nickel for hardness and aesthetics, gold for electrical contacts, chromium for hardness. Conversion coatings like alodine or black oxide pass salt spray for shorter durations but add no thickness.
Polishing and brushed finishes
Mechanical polish takes a part from Ra 1.6 µm to mirror (< 0.1 µm) at significant cost. Brushed finishes (#3 to #4) are common on stainless visible faces and look uniform once oriented with the grain.
Use the standardized triangle symbol with Ra value on the drawing instead of generic notes like 'polish'. This avoids back and forth during inspection.
Material and finish compatibility
| Material | Compatible finishes |
|---|---|
| Aluminum 6061/7075 | Anodize II/III, alodine, powder coat (over alodine), bead blast, brushed |
| Stainless 304/316 | Bead blast, brushed, mirror polish, electropolish, passivation |
| Mild steel | Powder coat, zinc plate, black oxide, paint |
| Brass | Polish, lacquer, nickel plate |
| Copper | Polish, lacquer, nickel/silver plate |
How to upload the finish spec
On Uretyco the finish dropdown is mapped to standard processes. Anything custom (specific RAL color, specific gloss, post-anodize sealing) should be added in the project notes plus the drawing. Our DFM agent flags incompatibilities before quoting.
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