What Is Hard Coat Anodizing

What Is Hard Coat Anodizing?

Hard coat anodizing is a method of anodizing aluminum. Anodizing is an electrochemical process that converts surface aluminum to aluminum-oxide. Anodizing improves the metals resistance to corrosion, wear and increases durability. Hard coat anodizing further enhances these properties.

Hard Coat Anodizing

Anodizing is designated as Type I or Type II. Hardcoat anodizing is referred to as Type III anodizing.

The Hard Coat Process

Hard anodizing or hard coating uses a sulfuric acid electrolyte to convert the aluminum surface to aluminum oxide. The sulfuric acid bath is approximately 32 degrees F, with a current density of 23 to 37 amps. The time to hard coat is from approximately 20 minutes to 2 hours. The alloy and coating thickness determines the amount of time.


Aluminum alloys will accept anodizing. Alloys higher in aluminum with less copper and silicone will accept the hard coat process better. The type of alloy changes the rate the coating builds up.


Hard coat anodizing colors aluminum gray. It can also be dyed, but the colors don’t come out as vibrant as they do with Type I or II anodizing.

Benefits of Hard Coat

Hard coat anodizing gives several advantages over anodizing. Among them, the metal is less resistant to abrasion, wears better, is harder and resists corrosion.