Anodizing is the process of creating an aluminum oxide coating by making an aluminum part anodic while suspended in an electrolyte. The electrolyte most commonly used is 15% by weight sulfuric acid; however chromic acid is sometimes used for aircraft parts. The process takes anywhere from thirty minutes to one hour, and the thickness ranges from .3 mils to 2 mils. The aluminum oxide coating that is produced is porous by nature and has the ability to adsorb dye or exhibit an excellent anchor profile for paint. It can be also be sealed if these properties are non-desirable. Below is the most common specification for anodizing.
Type I - Chromic Acid
Chromic anodize is the thinnest and softest anodic film, and is used primarily in military and aerospace applications that require strong corrosion resistance and adhesive bond ability. Chromic acid produced films are more dense, very thin (.2 to .5 mils), and darker in color. This process is utilized for corrosion protection rather than decorative purposes. Use of the chromic acid process may be advantageous where there is a possibility of solution entrapment in holes or cavities in pieces to be coated. Entrapment of sulfuric acid, as may occur in the case of the conventional sulfuric process, may adversely affect the service of the part.
Type II - Sulfuric Acid
Class 1 – Clear
Sulfuric acid anodizing produces an oxide coating on aluminum alloys that increases corrosion resistance and may also be used as a base for paint coatings. Other uses are for limited abrasion resistance, electrical insulation and for decorative purposes. Conventional sulfuric acid anodizing is most useful making aluminum parts more attractive and more corrosion resistant. The natural appearance of the aluminum oxide film is near transparent, and left as-is, it is known as clear anodizing. This is the most economical form of anodizing. The typical thickness ranges from .3 to .7 mils.
Class 2 – Color Dye
Color anodizing can make your products much more appealing, and is also useful for color-coding parts that look very similar but may have different uses or dimensions. IMF offers Black, Red, Blue, Green, Gold, and Yellow to suite your color anodizing needs.
Type III – Hard Anodize
Class 1 – Non Dyed
Class 2 – With Colored Dye
Hard Coat anodizing on aluminum alloys produces a hard and dense finish. It is an aluminum oxide coating, which provides good abrasion resistance, dry electrical insulation and also provides excellent corrosion resistance. Tests indicate that the hardness of this finish is about that of nitrided steel or file-hard, about 65 Rockwell on the C scale. The standard thickness is 1.5 to 2.5 mils, approximately one-half surface build up and one-half material penetration.