Aluminum is a remarkable material. Its unique combination of properties makes it suitable for many different applications. When exposed to air aluminum instantly forms a natural, thin, and transparent oxide film on the metal’s surface. This film provides a corrosion resistant barrier. The film will instantly re-form whenever the metal is cut or abraded. For many applications this glass-hard protective layer is all the surface finishing aluminum needs.
There are, however, circumstances where it may be necessary to add an additional protective or decorative finish to your aluminum extrusion profile. Choosing the correct finish is a key step in this process. The wrong surface finish can look aesthetically off or fail to protect the metal, which results in accelerated corrosion and possible structural issues. It is important to work closely with your aluminum extrusion manufacturer for the best advice on choosing the ideal surface finish for your particular needs.
Why Add a Finish to Your Aluminum Extrusion?
There are three main reasons for applying an additional finish to your aluminum extrusion: improving corrosion resistance, priming the surface for coating or paint, or enhancing the appearance of the aluminum.
Environmental Protection: The natural oxide film on the aluminum serves to protect it from corrosion, but in extreme environments extra protection may be needed. Extremes variations of moisture, humidity, and temperature can accelerate corrosion; as can use near ocean environments. In these instances, an added finish can help mitigate these environmental effects on the metal.
Metal Preparation: An additional finish may also be needed if you want to prepare the metal surface for coating or paint. Anodizing is an electrical process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases aluminum’s natural resistance to corrosion and increases the wear protection of the aluminum.
Enhanced Appearance: Finishing may also be required for aesthetic reasons, particularly in consumer products where appearance is often the first requirement. Depending on the look you are trying to achieve—you may want a brightly colored finished product, a mirror finish, or a textured look—different techniques can be applied.
What Types of Finishing Techniques are Available?
It is important to bear in mind that the choice of surfacing affects the price of the finished product. The finer the surface, the higher the production cost. While there are hundreds of different kinds of surface finishing, most typically fall into five distinct categories:
- Mechanical finishes are used to add texture to a surface or polish it to a chrome finish. Techniques include sanding, polishing, grinding, buffing, or blasting.
- Chemical finishes are applied by dipping the profile in a chemical mixture. The most popular chemical finishes include etching, which yields a frosted surface appearance, and bright-dipping, which produces a very shiny, specular (mirror) finish.
- Anodizing is a process in which the aluminum profile is immersed in a tank containing an acid-based electrolyte. The anodizing process allows aluminum profiles to retain their metallic luster while accepting durable and vibrant color.
- Liquid coatings are available in a broad range of paints, such as polyesters, acrylics, siliconized polyesters, and fluoropolymers. These applications are available in a nearly unlimited array of colors allowing for finishes that please every taste.
- Powder coating applies a decorative finish similar to paint but with more durability. The process involves melting dry plastic powder onto the metal to produce a textured, matte or glossy coating. Unlike liquid paint, no solvents are used so only negligible amounts of VOCs are released into the air, making it virtually pollution free. In addition, unused or over-sprayed powder can be recovered so any waste is minimal and can be disposed of easily and safely.
Whatever end-result you seek, your aluminum extrusion manufacturer can help you choose the right technique so your finished product is durable and visually pleasing.