1. Our equipment requires a variety of finishes. How versatile are extruded aluminum's finishing qualities? Extruded aluminum accepts a wide range of finishes unmatched by many materials. The natural protective oxide coating with its attractive metallic hue can be colored with a variety of chemical or anodizing processes. Surface textures can be created, from rough to matte to mirror-smooth. And surface coatings such as paint, lacquer, enamel, electroplating or laminates can be applied.
2. Is alloy selection important if I plan to have my extrusions painted or anodized? Yes. Alloys 6061, 6105 and 6063 are best suited for painted applications. Alloy 6063 is also routinely anodized. Special anodized finish such as "bright dip," however, should use alloy 6463. Since painting is a different process than anodizing, keeping your extruder informed of finishing requirements will result in better advice in all areas of your order.
3. How can I be assured of good adhesion when applying paint or lacquer to my extrusions? As with any other type of material, the surface should always be cleaned and pretreated as required for your specific coating. Before applying the top coat of paint or lacquer, the aluminum should be given a chemical conversion pretreatment, followed by a primer coat. This not only provides good adhesion, it also gives maximum corrosion protection.
4. What is the difference between a sulfuric acid anodize, hard anodize, and conversion coating? In the sulfuric acid anodizing process, the aluminum workpiece is placed in an acid-based electrolyte. An electric current is then passed through the part. During the oxidation process, the workpiece is coated with a hard, porous oxide layer. Organic coatings or dyes of various colors can thus be applied to the aluminum outside surface. The primary difference between the sulfuric acid anodize and hard anodizing processes are the operating temperature and the current density at which the process occurs. Hard anodizing produces a heavier coating with better wear properties than a sulfuric acid anodize. The conversion coating, also known as chrome phosphate or chrome oxide (yellow chrome), is a process that treats the metal surface as a result of chemical attack occurring when the metal is immersed in, or sprayed with, various solutions. This finish provides protection and good adhesion, but would typically be used as a base for another final finish.
5. What is etching? Etching is a chemical finishing process that produces a silver-white surface, often referred to as frosted or matte. In the etching process, the aluminum extrusion is passed through a warm chemical solution that removes the natural oxidation which has formed since extruding. It's then rinsed, and passed through a nitric acid bath, or desmutting process, to remove undissolved surface alloy constituents or impurities, and rinsed again. Then, to preserve its appearance, the extrusion is usually anodized.
6. I'd like my extrusion to have a shiny finish. Can this be done? Yes. With a chemical finishing process called bright-dipping, a special dip solution made of hot phosphoric acid and nitric acids is applied to the extrusion. The resulting finish is mirror-shiny, providing a highly reflective surface.
7. Can the natural corrosion resistance of extruded aluminum be increased? Yes, by a process known as cladding, whereby an additional layer of pure aluminum or appropriate alloy is applied to the surface of a strong aluminum alloy to increase corrosion resistance.

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