Type III

Type III hardcoat anodizing forms a thick, dense aluminum oxide layer for high wear resistance, hardness, and corrosion protection on aluminum parts.

Overview

Type III hardcoat anodizing is an electrochemical process that builds a thick, dense aluminum oxide layer, typically 0.0005"–0.003" total, on aluminum parts. It delivers high surface hardness (often 60+ HRC equivalent), strong abrasion resistance, and improved corrosion performance. The resulting layer is tightly bonded to the base metal and can be left unsealed for wear and lubrication or sealed for maximum corrosion resistance.

Use Type III when surfaces see sliding contact, abrasion, or impact, or when you need high durability in harsh environments. Expect limited color options (usually dark gray to black), longer lead times, and stricter process control than decorative anodizing. The coating adds thickness and affects fits, so you must account for dimensional growth, masking of critical areas, and potential post-machining. When correctly specified, Type III is a robust, repeatable finish for demanding aerospace, defense, industrial, and automotive applications.

Common Materials

  • Aluminum 6061
  • Aluminum 6082
  • Aluminum 7075
  • Aluminum 2024
  • Aluminum 5052
  • Aluminum 5083

Tolerances

—

Applications

  • Sliding wear surfaces on actuators and cylinders
  • Firearm receivers and slides
  • Robotic and automation wear rails
  • Hydraulic and pneumatic valve bodies
  • Aerospace hinge arms and linkages
  • Industrial tooling and fixtures requiring abrasion resistance

When to Choose Type III

Choose Type III anodizing for aluminum parts that see heavy wear, sliding contact, or frequent handling and require long life. It fits low to high production volumes where consistent abrasion resistance, surface hardness, and corrosion protection matter more than appearance or bright colors.

vs Type I

Pick Type III over Type I when wear resistance, surface hardness, and abrasion performance are critical, not just corrosion protection. Type III’s much thicker, denser oxide layer better protects surfaces in sliding or impact conditions and supports tighter, more durable fits on functional features.

vs Type II

Choose Type III instead of Type II when the part is functional rather than decorative and must survive heavy mechanical wear or aggressive environments. Type III provides a thicker, harder coating with superior abrasion resistance, accepting the tradeoffs of darker color, more limited aesthetics, and tighter process constraints.

vs Powder coating

Select Type III over powder coating when you need a thin, hard, dimensionally controlled wear surface instead of a thicker, more cosmetic protective layer. Type III is better for tight-tolerance mating parts, bores, and precision mechanical components where coating thickness and hardness directly affect performance.

vs Electroless nickel plating

Use Type III rather than electroless nickel when staying with aluminum-only surfaces is preferred and you want an integral oxide layer instead of a deposited metal. Type III typically offers excellent wear resistance with less risk of flaking or chipping on impact, provided the alloy and geometry are suitable.

vs No anodizing (bare aluminum)

Specify Type III instead of leaving parts bare whenever aluminum will see repeated motion, abrasion, or corrosive exposure. The hardcoat layer greatly extends service life, reduces galling in aluminum-on-aluminum contact, and can support higher loads and tighter fits without rapid surface degradation.

Design Considerations

  • Specify hardcoat thickness range and clearly indicate which dimensions are before and after anodize so shops can plan stock and post-machining if needed
  • Call out masking requirements on a dedicated drawing layer, including threads, precision bores, sealing surfaces, and electrical contact areas
  • Avoid very sharp edges and burrs; break edges (0.005"–0.015") to promote uniform coating and reduce chipping at corners
  • Design generous radii and avoid deep, narrow blind holes where solution flow and uniform coating thickness are difficult to achieve
  • Specify alloy and temper on the drawing; hardness, color, and achievable thickness depend heavily on the aluminum grade
  • For close-tolerance fits, model and tolerance diameters to account for coating growth on each surface or plan to ream/hone after anodize where practical