Pioneer Metal Finishing

View Comparison between Type II and Type III Anodize. (PDF)

Anodizing

• MIL-A-8625 Type II, Class 1 & 2
• AMS 2471 & AMS 2472

Anodizing (conventional Type II sulfuric anodizing) improves the performance of your parts for:

• Wear Resistance
• Lubricity
• Dielectric Properties
• Heat Dissipation
• Corrosion Resistance
• Bonding
• Aesthetics, ideal for producing intense colors

During sulfuric anodizing, no metallics are involved other than aluminum. Unlike electro-deposited metallic plating, where plating builds up by depositing on a base metal, an anodic coating penetrates and grows on the base metal by converting aluminum to aluminum oxide. The ratio of growth/penetration for anodic coatings is typically 50/50*. (*For critical applications, please consult with your Pioneer Metal Finishing sales engineer). See the growth/penetration

Proper formation of aluminum oxide coatings provides aluminum with a natural decorative appearance and increased resistance to corrosion and abrasion. Normally between .0001" to .001"; thick, sulfuric anodizing lends itself readily to clear and color work, as the coating is more transparent than other types of anodizing. In addition, it serves as a base for color absorption to create decorative finishes. Dyes can be deposited into the pores of the anodized layer and then sealed. The result is a highly desirable, rich, intense, permanent color finish.

Aluminum can be anodized and dyed to match a given decor or to assimilate a particular metal. Please visit the Dye Anodize page.

Click here to view our selection of dye colors

Microscopic view of surface pores in anodic coatings.

The Anodizing Process

Anodizing entails the immersion of an aluminum part in an electrolyte where an electric current is passed through the part. The surface is converted to aluminum oxide — one of the hardest substances known.

Proper formation of aluminum oxide coatings provides aluminum with a natural decorative appearance and increased resistance to corrosion and abrasion. In addition, it serves as a base for color absorption to create decorative finishes.

Sealing

The final treatment of clear or dyed anodized aluminum is sealing to close the pores of the aluminum oxide and render the coating non-absorptive. Sealing is accomplished by immersion in deionized water containing either nickel acetate, nickel fluoride, sodium dichromate or near boiling ionized water (water chemically distilled to a high degree of purity).

Sealing hard coat yields:

• Increased Corrosion Resistance
• Better Lubricity
• Better Light Fastness
• Better Weather Fastness

Alloys And Castings:
The Effects on Anodizing Processes

Each alloy anodizes differently because alloy metals change the conductivity of the part and cause it to form aluminum oxide, either faster or slower. All aluminum can be anodized, but some alloys work better than others. Castings tend to give the anodizer the most problems because of the porosity in the castings and alloying materials used. For applications requiring maximum corrosion protection, see Pioneer Metal Finishing's new breakthrough finish, EnduraGuard™.

Properties

Sulfuric anodizing has superb dielectric strength, good abrasion resistance, and excellent corrosion resistance. Type II anodizing is mostly used for decorative anodizing as it lends itself to the dying of light and dark colors, depending on the coating thickness. Where a colorless film is important, as for ornamental purposes or reflectors, Type II anodizing is used. There are some disadvantages to consider when contemplating the sulfuric acid process. The following types of parts should be avoided due to the corrosion nature of sulfuric acid: assembled parts, parts containing welds, joints, and recesses in which the anodizing solution may be retained.

Compatibility

Anodized aluminum is very compatible with other metals due to its dielectric qualities. Aluminum oxide minimizes galvanic corrosion where aluminum touches other metals.

Capabilities

Pioneer Metal Finishing can handle parts to maximum length of 156" x 60" x 30".

© 2007, Pioneer Metal Finishing