Anodizing is an electrochemical conversion process, not an applied coating. The surface of the aluminum metal is converted to aluminum oxide as a result of reactions occurring at the anode in a acidic solution. The anodized coating is formed by applying a D.C. Voltage to the aluminum while it is immersed in an acidic bath. To learn more about composition of the anodizing baths and more technical info open this file Anodizing tech info At Arnold’s Metal Finishing, whether aluminum is anodized by the piece or in batches, we summed up the process simply as a three-stage operation:
1: Pre-treatment: the aluminum surface must be prepared for the oxidation process by cleaning,etching, or bright dipping.
2: Anodizing: this is where the oxide film is actually developed.
3: Post-treatment: it is during this phase that color can be impregnated and sealing takes place.
The aluminum is now ready for fabrication or installation. It is more resilient, more attractive, and more versatile than
it was originally.
Regular Type II sulfuric anodizing provides these surface attributes:
• Corrosion Resistance (336+ hours salt spray resistance per ASTM B117)
• Moderate Durability
• Excellent Dye-ability (yielding deep, rich colors)
• Electrical Insulation
• Unlike paint, which can flake off if not applied properly,anodized aluminum finishes are actually formed from the original material and cannot flake off.
** Hot water seals produce the clearest sulfuric anodize while sodium dichromate yields a yellow-green appearance but is generally a better seal.