Understanding the Process
Aluminum extrusions are anodized to delay corrosion, improve lubrication, and allow for colour dying in a process that converts aluminum electrochemically. According to the Aluminum Anodizers Council (AAC), “the anodic structure originates from the aluminum substrate and is composed entirely of aluminum oxide. This aluminum oxide is not applied to the surface like paint or plating, but is fully integrated with the underlying aluminum substrate, so it cannot chip or peel.” The process of anodizing involves four steps that result in a wide range of aesthetic looks.
Step 1: Pre-treatment
The first step in anodizing includes pre-treating the aluminum through degreasing and pickling and providing a visible finish. Either bright or satin finishes can be applied to produce the desired effect. Satin finishing involves light etching to produce an even, matte surface on the aluminum. Bright finishing involves cleaning any heavy metal residue from the aluminum that was not removed during the pre-treatment processes. Bright- and satin-finished aluminum extrusions provide a smooth, clean surface for anodizing.
Step 2: Anodic oxide
The anodizing process requires submersion of the material in an acid electrolyte bath while an electric current passes through. The AAC notes that the “aluminum acts as an anode, so that oxygen ions are released . . . to combine with the aluminum atoms at the surface.” This process is a form of controlled oxidization during which the metal is chemically altered to the desired level. After the aluminum is anodized, colours can be applied using several methods.
Step 3: Colour anodizing
There are several techniques for colour anodizing aluminum. One technique is electrolytic colouring, which involves immersing the anodized aluminum in an inorganic metal salt bath. An electric current is applied to this bath as the metal salts oxidize in the aluminum’s pores. Depending on the chemical conditions of the bath and the length of time immersed, the aluminum colour will vary. Popular anodized colour finishes include gold, black, stainless, clear, brown, bronze, and nickel. Some companies using advanced technology also offer colour matching and custom colour anodizing.
Step 4: Sealing
The final step of the anodizing process is sealing the aluminum to prevent corrosion and water leakage. Sealing the anodized aluminum extrusions can be done in three ways: a cold method, a hot method, or a combination of the two. This also prevents any scratching or staining of the surface.
According to the AAC, there are a number of significant benefits to anodizing aluminum. These include durability, as anodized aluminum contains a reacted finish that is embedded in the metal, and the fact that anodizing ensures colour permanence and provides visually appealing alternatives to traditional aluminum. Anodized aluminum has lower process and maintenance price tags and is a long-lasting product. The most common uses of anodized aluminum are in appliances, food preparation equipment, artwork, furniture, and sporting goods, according to the AAC. Anodized aluminum has also been used in the manufacturing of trusses and handrails for the NASA Space Station. For more information about anodized aluminum extrusions and services, visit Dajcor.com