Hard Coat Aluminum Anodizing

What is Hard Coat Anodizing?

Aluminum hard anodizing, also known asMIL-A-8625Type III or engineered anodizing, is similar to standard anodizing in that both are controlled electrochemical processes. The key difference is that hard coat aluminum anodizing provides a surface that is more wear resistant and has a smoother and harder finish than standard anodizing. Hard anodizing is commonly performed clear or with a black dyed finish, though some prefer the aluminum dyed different colors for aesthetic purposes.


During the engineered anodizing process, a uniform aluminum oxide layer is formed on the surface that penetrates the material. The hard coat anodizing process involves submerging the part(s) in a sulfuric acid bath at approximately 32°F, with a density of 23 to 37 amps, for anywhere from 20 minutes to two hours. The amount of time spent submerged determines the thickness of the coating.

While aluminum naturally forms oxide on the surface over time, the aluminum oxide that is formed on the surface during the Type III anodizing process is more uniform, dense, and much harder than with natural oxidation.

Arrow Cryogenics offers aluminum hard coat anodizing (Type III) for dyed and non-dyed parts at our state-of-the-art facility in Blaine, Minnesota. We also provide standard aluminum anodizing (Type II) services. Contact us today or request a quote for anodized aluminum parts.

Benefits of Hard Anodizing

Arrow Cryogenics hard coat anodized aluminum has a thick coating that meets Military Standard Specifications MIL-A-8625 and is available in Type III Class 1 (Non-Dyed) and Class 2 (Dyed) options. Aluminum is a lightweight and versatile material that provides strength and corrosion resistance for a range of applications. Hard anodizing improves aesthetics and further increases the strength and corrosion resistance of aluminum parts.

Additional benefits of engineered anodizing include: 

  • Easier to clean and maintain
  • Dielectric properties
  • Improved lubrication
  • Resistance to peeling, flaking and chipping
  • Increased abrasion resistance
  • Flame resistance
  • Non-contaminating (for medical instrumentation)


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How Thick Is Hard Coat Anodizing?

The typical thickness produced by engineered anodizing MIL-A-8625 (Type III) is .0005”-0.002”, but the coating thickness can be controlled with exceptional accuracy using a state-of-the-art control system.

The coating created by Type III anodizing penetrates 50% of the surface, with the remaining 50% of the coating building up on the surface. Since hard anodizing alters surface thickness, it’s important to note that the process will affect the final dimensions of parts with tight tolerances.

When setting up an engineered anodizing project, Arrow Cryogenics makes sure that the required specifications are included in the work contract documents. We work closely with our customers when tight tolerances are required to ensure that the thickness of the anodized coating is exactly as expected.

Hard Coat Anodizing Colors

The color of the aluminum after being hard coat anodized depends on the alloy and the thickness of the coating. On some alloys, the color of non-dyed (Class I) aluminum after hard anodizing will change to a gray/bronze color; on others the aluminum will turn gray-black. If the aluminum is dyed (Class II), black is the most commonly used color.

Other hard anodizing colors may be available, but selections are limited and based on the alloy and the coating thickness. Sampling is required by Arrow Cryogenics if a color other than black is needed.

Contact us to learn more about Type III anodizing or request a quote for anodized aluminum.

Sealing After Hard Coat Anodizing

After an aluminum part has been hard coat anodized, there is an option to have it sealed. If the main function of the application is to obtain the maximum degree of abrasion or wear resistance, the coating should not be sealed. If the main function of the application is for corrosion resistance, and reduced abrasion resistance is not an issue, sealing is advised. If it is needed, the sealing of anodized parts must be specified by our customers.

NADCAP Certified

Arrow Cryogenics is Nadcap certified for chemical processing and is in compliance with the AC7004 Aerospace Quality System for the Aircraft, Space and Defense Industry. As part of Nadcap accreditation, our processes were audited based on stringent industry guidelines and are regularly reviewed to maintain compliance.

Contact us to learn more about our Nadcap certification or to discuss finishing services for your aerospace application.

Request a Quote for Aluminum Hard Anodizing

Hard anodized aluminum offers low-maintenance durability and can be used for a wide range of applications. Various industries benefit from the use of anodized aluminum parts, including: 

  • Automotive
  • Aviation & Aerospace
  • Buildings & Architecture
  • Electronics
  • Food Manufacturing / Preparation
  • Equipment
  • Home Furnishing
  • General Manufacturing
  • Marine Industry
  • Medical / Dental Equipment
  • Military / Law Enforcement
  • Sporting Goods

Arrow Cryogenics is an ISO 9001:2015 and Nadcap certified for chemical processing company offering aluminum anodizing and more. Please contact us for more information or request a quote for Type III anodizing services.