Hard Anodizing

Hard anodizing, also known as hard coat (or hardcoat) anodizing, is Type III aluminum anodizing. Standard aluminum anodizing is Type II anodizing.

Hard anodizing is very similar to standard anodizing. Both are controlled chemical processes used to increase corrosion resistance and surface hardness, allow dyeing, and/or improve lubrication or adhesion of aluminum and aluminum alloy materials. Hardcoat anodizing can be thought of simply as a “heavy duty” form of standard anodizing.

In hard coat anodizing, an anodic film forms on the part by converting its surface into aluminum oxide. Aluminum naturally self-passivates when exposed to oxygen, creating an oxide layer approximately 2 to 3 millimeters thick. Alumiunum alloys form oxide layers from 5 to 15 millimeters thick through self-passivation. Hard anodizing aluminum and aluminum alloy materials greatly increases the thickness of the oxide layer. Different hardcoat anodizing processes produces oxide layers of different thicknesses, and can be somewhat customized to provide the optimum results for the treated material’s specific application.

Benefits of Hard Anodizing

Hardcoat anodizing provides numerous benefits that can improve the treated aluminum’s performance, aesthetics, or both.

  • Improved corrosion resistance
  • Better surface finish quality
  • Improved dielectric properties—the anodic layer produced is non-conductive
  • Dyeable/colorable
  • Increased abrasion resistance
  • Flame resistant
  • Improved wear resistance

Hard Anodizing Standards

Hard coat anodizing is regulated by a number of national and international standards, including MIL-A-8625, AMS 2482 (formerly MIL-A-65376), AMS 2468C (equivalent to SAE 8625), ISO 10074:1994, and BS 5599:1978 (British Standard).

Hard Anodizing Providers

  • Arrow Cryogenics, Inc., of Blaine, Minnesota, provides both hard anodizing and Type II standard aluminum anodizing services. They are an ISO 9001:2008 certified company with over 30 years’ experience in anodizing and other surface finishing processes.
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