Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light. Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodic films are most commonly applied to protect aluminum alloys, although processes also exist for titanium, zinc, magnesium, and niobium.
Anodization changes the microscopic texture of the surface and can change the crystal structure of the metal near the surface. Coatings are often porous, even when thick, so a sealing process is often needed to achieve corrosion resistance. The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit. Anodized aluminum surfaces, for example, are harder than aluminum but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, making them less likely to crack and peel.
Aluminum alloys are anodized to increase corrosion resistance, to increase surface hardness, and to allow dyeing (coloring), improved lubrication, or improved adhesion.
When exposed to air at room temperature, or any another gas containing oxygen, pure aluminum self-passivates by forming a surface layer of amorphous aluminum oxide 2 to 3 nm thick[3] which provides very effective protection against corrosion. Aluminum alloys typically form a thicker oxide layer, 5-15 nm thick, but tend to be more susceptible to corrosion. Aluminum alloy parts are anodized to greatly increase the thickness of this layer for corrosion resistance. Many aluminum aircraft parts, architectural materials, and consumer products are anodized. Anodized aluminum 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 anodizing only has moderate wear resistance, the deeper pores can better retain a lubricating film than a smooth surface would.
Gayston currently anodizes using a sulfuric acid solution which is the most widely used to produce anodized coating, and is capable of producing thin, medium, and thick anodize coatings. With the thinner coating used for moderate corrosion resistance and ability to color the aluminum and the thicker coatings used for hard anodizing to increase surface hardness, lubricity, and corrosion resistance.
