Anodize & Hardcoat Anodize

Under EPA rules, anodizing is an environmentally friendly process that generates zero hazardous waste.

Aluminium alloys are anodized to increase corrosion resistance, to increase surface hardness, to allow dyeing (coloring), allow improved lubrication, and improve surface adhesion. The anodic layer is non-conductive.

PROTECTING ALUMINUM FROM WITHIN

(Type II Sulfuric Acid Anodizing & Type III Hard Coat Anodizing)

The anodize process refers to the passing of DC current through an aluminum part (the anode) while the aluminum part is submerged in a sulfuric acid electrolyte bath.  Contrary to some beliefs, anodize is not metal plating or a surface paint. The anodize process results in a durable layer of aluminum oxide being rooted into and grown on the surface of the part. This layer is porous and receptive to dyeing.  Aluminum oxide’s hardness levels are just slightly less than that of a diamond. The end result is an aluminum product with extended life.  The difference between anodize and hardcoat anodize is that the hardcoat anodize process takes place at lower electrolyte bath temperatures and requires greater DC current.  Hardcoat anodizing will produce oxide thicknesses up to 75 μm thick while type II is limited to approximately 25 μm.  The density of hardcoat anodize results in the coating being less porous and less receptive to dye or coloring treatments, but it dramatically increases wear resistance and corrosion protection versus conventional Type II anodize.  Type II anodizing on the other hand is many times more receptive to coloring in multiple colors and is the most common form anodizing.

When exposed to air at room temperature, or any other gas containing oxygen, pure aluminium self-passivates by forming a surface layer of amorphous aluminium oxide 2 to 3 nm thick, which provides very effective protection against corrosion. Aluminium alloys typically form a thicker oxide layer, 5-15 nm thick, but tend to be more susceptible to corrosion. Aluminium alloy parts are anodized to greatly increase the thickness of this layer for corrosion resistance. The corrosion resistance of aluminium alloys is significantly decreased by certain alloying elements or impurities: copper, iron, magnesium, and silicon, so 2000, 4000, and 6000-series wrought alloys and 300 series cast alloys tend to be most susceptible.

Some aluminium aircraft parts, architectural materials, and consumer products are anodized. Anodized aluminium can be found on mp³ players, flashlights, cookware, cameras, sporting goods, window frames,roofs, in electrolytic capacitors, and on many other products both for corrosion resistance and the ability to retain dye. Although Type II anodizing only has moderate wear resistance, the deeper pores can better retain a lubricating film than a smooth surface would.

In the PowderTech anodization processes, the aluminium oxide will grow down into the surface and out from the surface by equal amounts in hard anodizing and 35/65 in Type II anodizing. So anodizing will increase the part dimensions on each surface by roughly half of the oxide thickness. For example a coating that is (2 μm) thick, will increase the part dimensions by (1 μm) per surface. If the part is anodized on all sides, then all linear dimensions will increase by the oxide thickness. PowderTech provides both Type II and Type III anodizing and includes numerous colors for standard applications.