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Anodizing

Created through electrochemical conversion, anodizing is used to increase durability of a component, prevent tarnishing and to maintain a component’s cosmetic appearance. Frequently used on aluminum for both strengthening and aesthetic purposes, anodizing both penetrates and builds on the surface at an approximately 50/50 ratio.

Type I (Chromic Acid) Anodizing

Chromic Acid anodizing is a metal coating process used when the application calls for a thin coating and a high level of corrosion resistance. Type I is achieved by a chemical conversion processes involving immersion of an aluminum component in a chromic acid bath.

Type I anodizing is used in high stress applications, primarily in aerospace applications. It is generally used as a base for paint or adhesives or can be used as a mask for Type III (Hardcoat) anodizing.

  • Corrosion resistance
  • Dielectric for electrical resistance
  • Adds very thin anodic layer (usually approximately 0.0001 inch)
  • MIL-A-8625F type I
  • MIL-STD-171D
  • AMS 2470
  • Masking
  • In-house salt spray testing
  • In-house NDT testing
  • Normal turn time is three to five working days (without masking)
  • Masking may increase turn time
  • Expediting available, when possible for an additional fee

Type II (Sulfuric or Color) Anodizing

The most common type of anodizing is sulfuric acid anodizing, also called decorative or color anodizing since it produces a porous surface which accepts dyes easily. The process essentially speeds up the natural oxidation of aluminum by placing an object into a bath of sulfuric acid and running an electric current through the solution. Dyed anodizing is usually sealed to reduce or eliminate dye bleed out.

Sulfuric anodizing is used widely used across all industries for general and commercial aluminum anodizing. Type II anodizing is most commonly based on the military specification MIL-A-8625. In addition to military and defense applications, this designation is also standard for commercial use around the world for aerospace, automotive and medical industry segments.

  • Accepts dyes easily
  • Heat resistance
  • Corrosion resistance
  • Improved paint adhesion
  • Good electrical insulation
  • MIL-A-8625, type II, class I & II
  • AMS-2471
  • MIL-STD-171
  • Available in wide variety of dyed colors
  • Hot water or nickel acetate seals
  • Masking for selective anodizing
  • In-house salt spray testing
  • Normal turn time is three to five working days (without masking)
  • Masking may increase turn time
  • Expediting available when possible for an additional fee

Type III (Hardcoat) Anodizing

Type III (Hardcoat) anodizing forms a very hard, dense, and relatively thick coating. It is used whenever the application calls for a super hard surface. The process is similar to Sulfuric Anodizing, but the layer of aluminum oxide is produced at much higher voltage and cooler temperatures.

Hardcoat anodizing is generally not colored or dyed. However, a variety of shades from grey to black can be achieved by altering temperature, voltage and the chemical composition of the solution. Different aluminum alloys also yield different shades of gray. Hardcoat anodizing is used in in aerospace, marine, cookware, food processing and a wide variety of uses in other industries.

  • Highly abrasion resistant surface (60 – 70 Rockwell C)
  • Thickness ranges from 0.0005 – 0.003 inches (half build and half penetration)
  • Wears better
  • Corrosion resistance  
  • MIL-A-8625 Type III
  • MIL-STD- 171
  • AMS 2468
  • Variety of masking options
  • In-house Salt Spray testing
  • In-house nondestructive testing
  • Post anodize seals ( though these may decrease hardness)
  • Normal turn time is three to five working days (without masking)
  • Slightly longer turn time if intricate masking required
  • Expediting available when possible for an additional fee