Anodize Service
Resolute Precision Manufacturing coordinates surface coating and finishing for precision machined components through our qualified outside coating network. Anodize, black oxide, zinc plating, electroless nickel, and passivation we manage scheduling, shipping, quality inspection, and documentation so you receive fully finished, coated, ready-to-install parts from a single purchase order. Request a QuoteWhat Anodizing Does to Aluminum
Anodizing is an electrochemical process that converts the surface of aluminum into aluminum oxide a hard, porous ceramic layer that is integral with the base material rather than a coating applied on top. Unlike paint or plating, which can chip, peel, or delaminate, the anodized layer is chemically bonded to the aluminum and cannot separate.
The anodized layer provides substantially improved corrosion resistance compared to bare aluminum, increased surface hardness (Type III hard coat reaches Rc 60–70 on the surface), electrical insulation, and a uniform appearance that accepts dye for color finishing. The porous structure of the oxide layer allows dye molecules to penetrate and be sealed in producing colors ranging from clear/silver through black, red, blue, gold, and custom colors.
Type II vs. Type III Anodize
Two anodize specifications are used depending on the functional requirement:
Type II (conventional/decorative anodize) — produces a 0.0002″ to 0.001″ thick oxide layer; provides corrosion resistance and decorative finish; suitable for appearance applications and light-duty wear; available in all colors
Type III (hard coat anodize) — produces a 0.001″ to 0.002″ thick oxide layer; surface hardness Rc 60–70; significantly improved wear resistance; used for engineering applications requiring abrasion resistance; limited color options (natural, black)
Specifications
| Standard | MIL-A-8625 Type II and Type III |
| Type II Layer Thickness | 0.0002″ to 0.001″ (0.1 to 25 microns) |
| Type III Layer Thickness | 0.001″ to 0.002″ (25 to 50 microns) |
| Type III Surface Hardness | Rc 60–70 on 6061 and 7075 aluminum |
| Dimensional Impact | Type II: approximately net zero (50% penetration/50% build); Type III: builds approximately 0.001″ per side |
| Colors (Type II) | Clear, black, red, blue, gold, green, and custom colors; sealed with hot DI water or Teflon seal |
| Colors (Type III) | Natural gray to dark bronze; black dye available with limited decorative options |
| Alloy Compatibility | 6061, 6063, 7075, 2024, 5052, and MIC-6 cast plate; anodizing response varies by alloy |
| ISO | ISO 9001:2015; outside suppliers qualified under RPM’s approved vendor procedures |
Designing Aluminum Parts for Anodizing
Anodize layer thickness must be accounted for in dimensional design. Key considerations:
- Type III hard coat builds approximately 0.001″ per side — machine OD features 0.001″ per side oversize to allow for build
- Internal threads: tap after anodizing for Type II; for Type III, oversize tap before anodizing is common practice
- Sharp corners: anodize burns off sharp edges — add a minimum 0.010″ chamfer or radius on all edges
- Blind holes: ensure drain holes or feature orientation allows anodize solution to drain completely
- 2024 aluminum: anodizes with reduced corrosion resistance compared to 6061 or 7075 — consult us before specifying for corrosion-critical applications
Frequently Asked Questions
What aluminum alloys can be anodized?
Most aluminum alloys can be anodized. 6061 and 6063 produce the best results clear, uniform oxide layer with excellent corrosion resistance. 7075 anodizes well but with slightly reduced corrosion resistance. 2024 anodizes with difficulty and produces lower quality results often only suitable for Type I (chromic acid) anodize. Cast alloys (A380, 356) can be anodized but produce non-uniform results due to silicon content.
Does anodizing change the dimensions of my part?
Type II anodize grows approximately 50% of the layer thickness outward and consumes 50% inward net dimensional change is approximately zero for most precision fits. Type III hard coat builds approximately 0.001″ per side outward. Critical mating dimensions should be machined to pre-anodize dimension accounting for this build.
Can anodizing be applied to only part of a surface?
Yes. Masking with plugs and tape prevents anodizing on specific surfaces. Common masked areas include precision bearing fits, threaded holes, and mating faces where coating would affect assembly fit.
What colors are available for Type II anodize?
Standard colors include clear (natural aluminum appearance), black, red, blue, gold, green, orange, and purple. Custom colors are available through color matching to a reference sample or Pantone specification. Color consistency across lots is best maintained when specifying a standard color from the anodizer’s color chart.