Anodizing Color & Thickness Chart

Type II is a decorative and mildly protective anodize with a thickness of 0.2 to 1.0 mils. It accepts a wide range of dye colors. Type III, also called hardcoat, is much thicker (1.0 to 4.0 mils) and significantly harder (400-700 HV). Type III provides superior wear and abrasion resistance but is limited to darker colors like black, dark grey, and natural.

Most aluminum alloys can be anodized. The 5xxx and 6xxx series (like 6061 and 5052) anodize best with uniform color. The 2xxx series (like 2024) and 7xxx series (like 7075) can be anodized but may show color variation due to high copper or zinc content. Cast alloys generally produce a less uniform finish than wrought alloys.

Anodizing grows both inward and outward from the original surface. Roughly 50% of the total thickness penetrates into the base metal and 50% builds up above it. For Type II at 0.5 mils total, expect about 0.25 mils per side of dimensional growth. For Type III at 2.0 mils total, expect about 1.0 mil per side. Account for this in your tolerancing.

Exact color matching is difficult because the final color depends on the alloy, temper, surface finish, and bath chemistry. Different alloys in the same batch can appear slightly different. For best results, use the same alloy and temper across all parts, and specify a color sample or Pantone reference for your anodizer to target.

MIL-PRF-8625 (formerly MIL-A-8625) is the governing specification for anodizing of aluminum alloys. It defines Type I (chromic acid), Type II (sulfuric acid), and Type III (hardcoat sulfuric acid) processes. It also defines Class 1 (non-dyed) and Class 2 (dyed) finishes. Most commercial and aerospace anodizing references this spec.