CNC parts rarely ship as-machined. Surface treatment improves wear, corrosion, appearance, and longevity. Here's a quick map of the 8 most common options.
For aluminum
- Anodizing (clear, color, black, etc.) — corrosion + decorative
- Hard anodizing (25-50 μm, HV 400+) — premium wear resistance, ~1.5-2× the cost
For stainless steel
- Passivation — nitric/citric acid bath; standard for medical, semiconductor
- Electropolishing — mirror finish + improved corrosion resistance
- PVD coating (TiN, CrN, DLC) — extreme wear, low friction; ~3-5× standard plating
For steel
- Blackening / bluing — cheapest, indoor only
- Nickel plating — versatile, good corrosion resistance
- Hard chrome plating — HV 800+, classic for hydraulic rods, dies
- Powder coating — RAL colors, thick (60-100 μm), for housings and structural parts
Decision priorities
Choose by material first, then by primary requirement (appearance / wear / corrosion / electrical), then by budget. The wrong treatment can fail in months; the right one extends part life 3-5×.
