Hardcoat Anodizing – Type III

[formed by using an electrolitic solution of sulfuric acid]

A.M. Metal Finishing:

  • MIL-Spec 8625F
  • Type III
  • Gray or Black
  • Uniform Buildup
  • Selective Masking
  • Teflon Coating Available
  • Dichromate Seal Available

Call A.M. Metal Finishing at 407-843-0182 for all your finishing needs.

Hardcoat Anodizing Services in Central Florida

Hardcoat anodizing is commonly referred to as Type III anodizing. Hardcoat is formed by using an electrolytic solution of sulfuric acid at approximately 32° F and a current density of 23 to 37 amps per square foot. The process time is determined by the alloy used and desired coating thickness. This will produce a gray or black coating.

Anodizing Benefits

  • Hardness: Sapphire Rockwell C60
  • Wear Resistance: 10x wear resistance of conventional anodizing
  • Uniformity: Precision control of close tolerances
  • Thermal Properties: Low thermal conductivity & minimized expansion
  • Heat Resistance: To the melting point of aluminum 1221º F
  • Corrosion Resistance: Excellent corrosion resistance

For more information concerning Anodizing, download our Hardcoat Anodizing Reference Guide in PDF format (file will open in a new window and requires Adobe Acrobat to print). Please contact us if you need further information.

Before and After Hardcoat Anodizing

Hover over the photo to see the before photo of a large pipe that was hard coat anodized.


How to Order Hardcoat Anodizing

To save time, trouble and possible errors, information on the following four (4) items must be known:

  1. Alloy
  2. Coat Thickness
  3. Masking Requirements (if any)
  4. Racking Instructions (if possible)

Alloy – Hard Coat can be applied to virtually any aluminum alloy. However, since the coating builds up at different rates on each alloy, in order to control coatings accurately it is important to specify the alloy. Also, some alloys require different procedures from others. If the alloy is not properly designated, there is a possibility of damage.

Coating Thickness – Hard Coat may be provided in thickness ranging from a few .0001’s to .008″ or .009″, depending on the alloy and the application. Like other coatings, Hardcoat changes the dimensions of the basic part. One-half of the Hardcoat buildup and one-half is penetration, i.e., .002″ hardcoat consists of .001″ penetration and .001″ added to the original dimension. Therefore, in machining the part, it is essential to allow for the change and to request a specific coating thickness on blueprints and/or purchase orders.

Masking – It may be necessary to exclude (or mask) the coating from certain areas of a part. If so, areas to be masked (threaded holes, bored holes, ground points, etc.) should be clearly specified. In designing for hardcoat, remember that masking is a hand operation which often, but not always, means added cost. For instance, even if Hardcoat is only required on one area of a part, it is usually much less expensive to permit the part to be coated all over if at all possible. On the other hand, it is usually less expensive to tap holes to a standard size and mask them rather than use oversized taps.

Racking – Firm electrical and mechanical “contact” must be made with every part to be hardcoated. That is, each part must be “racked.” Proper racking is key to economic and effective processing of parts. Since each rack contact point leaves a small void in the coating, it is essential that such contacts be made in non-critical areas. Any guidance which can be provided as to where best to rack the part will aid in proper processing.

Before designing a part for Hardcoat, if you have any questions as to how to handle your part, please call us. We will gladly advise you by telephone or make a personal visit.

Hardcoat Anodizing Points of Interest

  • MIL-Spec 8625F
  • Type III
  • Gray or Black
  • Uniform Buildup
  • Selective Masking
  • Teflon Coating Available
  • Dichromate Seal Available

Fun Fact

Type III, hardcoat, hard anodizing, or engineered anodizing require more process control, and are produced in a refrigerated tank near the freezing point of water with higher voltages than thinner coats. 

Did You Know?

Anodizing thickness increases wear resistance, corrosion resistance, ability to retain lubricants and PTFE coatings, and electrical and thermal insulation.

A.M. Metal Finishing offers Type II anodizing as well as Type III hard anodizing. Contact us at 407-843-0182 if you need assistance determining your anodizing specifications or have parts which require hard coat anodizing.

Contact Us

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7594 Chancellor Drive, Orlando, Florida 32809


Toll Free 1-888-663-6136

Fax 407-849-1724

Hours of Operation:

Monday - Friday
8:00 a.m. - 4:30 p.m.