What is Anodize?

Anodizing is an electrolytic process in which an oxide (anodic) layer is chemically built on the surface of the metal. This oxide layer acts as an insulator and provides surface corrosion protection along with an excellent substrate for decorative finishes. The anodic oxide structure originates from the aluminum substrate and is composed entirely of aluminum oxide. It has a highly ordered, porous structure that allows for secondary processes such as coloring and sealing.

Anodizing is a “conversion coating” & is very different than paint, electroplating & other metal coatings. Anodize coatings are measured by thickness – the term thickness includes both penetration & build-up. While paints and plating sit on top of the surface of the aluminum, anodizing converts the outer layer of aluminum to aluminum oxide, so the coating is fully integrated with the aluminum substrate. This is the primary reason why anodize thickness is defined by the combination of the penetration into the substrate & the buildup of the oxide layer from the original dimension.

Types of Anodize Provided by AOTCO:

Type I  – Chromic acid anodizing

Purpose: Anodizing process that is low stress on metal and provides a ductile surface finish. Works well as a base for paint. Used extensively in aerospace applications, particularly in castings. 

Type II   – Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath

Purpose: Intended to improve surface corrosion protection under severe service conditions or as a base for paint systems.

Type IIB  – Thin sulfuric acid anodizing, for use as non-chromate alternative for Type I and IB coatings

Purpose: Non-chromate alternative to Type I and IB coatings, where corrosion resistance, paint adhesion, and fatigue resistance are all required.

Type III  – Hard Anodic Coatings

Purpose: Provide wear and abrasion resistant surfaces with improved corrosion protection due to greater thickness and weight than the conventional anodic coatings. Sealing of Type III coatings is not recommended unless corrosion resistance is also a factor. Wear resistance is reduced by sealing. Fatigue strength can be reduced by Type III.

Type III is typically utilized in valves, sliding parts, hinge mechanisms, cams, gears, swivel joints, pistons, rocket nozzles, insulation plates, blast shields, etc.

Benefits of Anodize

  • Very price competitive with painting and powder coating.
  • Durable, hard, abrasion resistant, and long lasting. Coating does not peel or chip.
  • Excellent corrosion protection. Withstands salt-spray and other tests extremely well.
  • Good electrical insulator. Combined with other coatings can be used for selective masking of low-voltage cu.
  • Environmentally-friendly. Can be readily recycled. Inorganic chemicals used have minimal environmental impact.

At AOTCO, we specialize in Sulfuric Anodize & Hardcoat Anodize

Please visit our Sulfuric Anodize and Hardcoat pages for details about these processes