Type ΙΙ coatings are similar to a Class 2 AAMA specification (per MIL 8625F1)
Military Standards for Anodize
Type ΙΙ — Sulfuric Anodize
Type ΙΙΙ — Hard Coat Anodize
Class 1 — Non dyed (clear)
Class 2 — Dyed
(per AAMA 611-12)
Minimum .7 Mil thickness
Minimum 3,000 Hours salt spray resistance
Minimum .4 Mil thickness
Minimum 1,000 Hours salt spray resistance
A41 — Clear anodize
A31 — Clear anodize
A43 — Dyed color
A33 — Dyed color
A44 — Electrodeposited color
A34 — Electrodeposited color (2-step)
Types of Anodize
Anodize is an electro-chemical process that converts aluminum’s surface in a decorated, durable and corrosion resistant finish. The process works by racking the parts using either aluminum or titanium racks or clips to create solid electrical connectivity. The parts are dipped into a micro-etch cleaning tank to remove all oils and dirt, then rinsed. The next process is an etching tank which includes a sulfuric acid bath and rinse, followed by a de-smut and rinse to remove the etch residue and prepare the parts for anodizing. The parts are then anodized and rinsed. Anodizing is a caustic process that rapidly oxidizes the surface and leaves a clear film. Anodize works by engulfing the parts in an electrolyte acid bath and passing an electric current through the parts using cathodes in the anodize tank. The longer the parts are left in the anodize tank the thicker the film becomes.
(See below for typical anodize thicknesses and class, mil, or AAMA specifications)
Parts can also be anodized a color which absorbs into the clear film before the parts are sealed. Colored anodize parts are soaked in a dye tank then sealed on the aluminum. To eliminate fading, a 2-step anodize process is used where the aluminum is anodized then tin particle are bonded to the surface by using an electrolytic plating process.
The electric current pulls the tin particles to the part and gives the surface a rich non-fading color. 2-step anodizing can be done in a range of colors from light champagne to black finishes.
The benefits of anodizing over painting is the color fade retention in clear and 2-step finishing. There is a better corrosion resistance, and a high quality metallic look and feel of the part as well as better heat dissipation in electronics applications. Custom Aluminum Products is one of the largest anodizers in the Chicago Illinois area with over 30 anodize tanks in house and can anodize parts up to 24’ in length.
To learn more about all of our capabilities please contact our sales team for a copy of our Engineering Guide for Aluminum Extrusions.