Loading page
Anodize Type III (hardcoat)
Type III hard anodize is a sulfuric acid anodize run cold, near 32 °F (0 °C), at high current density to grow a dense, hard oxide. Coatings are typically 0.001–0.003 in (25–75 µm), with 0.002 in (50 µm) the MIL-A-8625 default, and about half builds above the surface. It gives high wear and abrasion resistance and electrical insulation. Natural color is gray to bronze.
- Applies to
- Wrought aluminum alloys, especially 6061 and 7075; high-copper and high-silicon alloys coat thinner and darker
- Adds
- 5 days
- Cost
- Moderate
Colors
- Natural (gray to dark bronze)
- Black (dyed)
Specs
| Coating thickness | 0.001–0.003 in (25–75 µm); 0.002 in (50 µm) default |
|---|---|
| Dimensional growth | About 50% of thickness per surface |
| Hardness | Typically 400–600 HV microhardness, alloy dependent |
| Wear resistance | Taber abrasion tested per MIL-A-8625 |
| Edge radius | Break sharp edges to at least 0.010 in (0.25 mm) to prevent chipping and burning |
| Fatigue | Reduces fatigue strength; evaluate cyclically loaded parts |
Call out on the drawing
- MIL-A-8625 Type III, Class 1 (undyed) or Class 2 (dyed)
- AMS 2469 (hard anodic coating)
- ISO 10074 (hard anodic oxidation coatings)
Common on
Questions
Type II vs Type III anodize?
Type II is thinner, 0.0002–0.001 in (5–25 µm), takes bright dyes, and is chosen for corrosion protection and appearance. Type III is 0.001–0.003 in (25–75 µm), much harder and more wear resistant, and comes in natural gray-bronze or black. Use Type III on sliding, wear or abrasion surfaces.
How much does hard anodize change dimensions?
About half the coating builds up per surface. A 0.002 in (50 µm) coating grows each face about 0.001 in (25 µm) and a diameter about 0.002 in. On 60° threads, pitch diameter grows about four times the build per surface, so threads need pre-plate sizing or masking.
Can hard anodize be dyed colors?
Black dyes well. Bright colors look muddy because the natural oxide is gray to bronze and dark. For bright colors, use Type II.
Does hard anodize reduce fatigue strength?
Yes. The hard, brittle oxide can initiate cracks and noticeably lower fatigue strength, especially on 7075 and 2024. On fatigue-critical parts, specify the thinnest coating that meets wear needs, or shot peen before anodizing.
Other finishes on these processes
Price it with this finish.
The builder adds lot charges, per-part cost and lead time for the finish you pick.