Anodized fasteners are used to connect metal parts in vehicles, aircraft, and boats. Anodizing is an electrochemical process that creates a hard finish on aluminum parts, making them strong and resistant to wear and corrosion. The process involves creating a layer of aluminum oxide on the surface of the parts, resulting in a very durable finish. Anodized fasteners are less prone to galvanic corrosion and can be colored to suit the user. Other metals can also be anodized, and different acid solutions can be used to provide a range of oxide coatings.
Fasteners can include nuts, bolts and washers used to connect metal parts. They are used as connectors in vehicles, aircraft and boats. Aluminum metal can be soft, making it difficult to use for attaching objects, as untreated metal can warp or break. A process called anodizing creates a much harder metallic finish, and anodized fasteners are both strong and resistant to wear or corrosion.
Anodizing is an electrochemical process, using both an electric current and an acidic chemical bath, to create a hard finish on anodized fasteners. The process involves creating a layer of aluminum oxide on the outside surface of the parts. Rather than a coating like paint, the anodized finish is a molecular bond with the underlying aluminum metal, resulting in a very durable finish.
The process uses an acid bath, which supplies oxygen for the chemical reaction. Anodized fasteners are connected to one side of an electrical circuit and a separate metal electrode is dipped into the bath. When the parts enter the acid, an electrical circuit is established and the aluminum parts are oxidized on the surface to form aluminum oxide.
Anodizing involves the rapid oxidation, or rusting, of the aluminum surface of parts. Unlike normal rust, aluminum oxide forms a very thin and hard crystalline structure which becomes a new surface. These surfaces can wear away over time, but can provide long life with minimal deterioration, particularly when compared to pure aluminum.
It is important when fastening metals to use the same metals for all parts, to avoid galvanic corrosion. This occurs when a small electric current passes between dissimilar metals, and softer metals such as aluminum can be damaged more quickly by galvanic action. In addition to reinforcing the metal, anodized fasteners are less prone to galvanic corrosion because the aluminum oxide finish can block electrical current.
Anodized fasteners are often used to customize automobiles and one reason is that the anodized finish can easily be colored to suit the user. The aluminum oxide finish is porous, meaning it contains many small voids or openings, rather than being perfectly smooth. These blanks can accept dyes or color pigments, allowing parts to be customized in a wide variety of colors. The color becomes a permanent part of the finish and no further painting is required to maintain it.
Other metals can be anodized, including titanium, which improves their corrosion resistance in aircraft applications where parts are exposed to wide temperature and humidity ranges. Different acid solutions can be used to provide a range of oxide coatings, depending on the specification of the part. Sulfuric acid is the most common type of anodizing and can create both thin and relatively thick coatings. Chromic acid is used when very thin coatings are needed, particularly for parts that require a very close fit, known as tight tolerances.
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