Hardcoat Anodizing

Hardcoat anodize, commonly referred to as Type III anodizing, 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 will run for 20 to 120 minutes depending on the alloy used and desired coating thickness. This will produce a generally gray coating 10µm to 50µm thick with 50% buildup and 50% penetration.

Properties

Hardcoat anodizing provides for several desirable qualities such as:

• Corrosion Resistance (336+ Hours salt spray resistance per ASTM B117)
• High Durability (file hard, 60-70 on Rockwell C-scale)
• Electrical Insulation (800 V / mil thickness)

Hardcoat anodize coatings may be dyed a variety of colors. However, due to its naturally darker appearance, dyeing does not produce the vibrant colors that a Type II sulfuric anodize will. Additionally, the required sealing process after dyeing does slightly reduce hardness.

Specifications

There are hundreds of governmental, industrial, and commercial anodizing specifications in use, each with their own method of calling out coatings, seals, dyes, etc. Any anodizer should recognize the Type III designation to indicate a hardcoat anodize, Class 1 to specify natural color or no dye, and Class 2 to indicate a dye.

Materials

Hardcoat anodizing works very well with 6000, 5000, and 7000 series alloys. High-copper 2000 series alloys can present some difficulties and should be avoided if possible. As with all forms of anodizing high-silicon die castings are not recommended.