R. A. Prado, Naval Aviation Depot, Jacksonville, FL

Summary:

Aluminum anodizing (formally known as “Anodic Coatings for Aluminum Alloys” under military specification (mil-spec) MIL-A-8625F) is an electrochemical oxidation process commonly formed on the surface of aluminum substrates. This process results in an anodic coating that is extremely durable, abrasion and corrosion resistant. Because of its porous nature, it can also be dyed to a variety of colors and/or later sealed to further increase its corrosion resistant properties. Formation of anodic coatings on aluminum substrates using traditional methods has been practiced for many years. These methods include manual operation/adjustments of the rectifier (power source) to supply required current to the work piece, the use of lead cathodes, copper bus bars, and sulfuric acid as the common electrolyte. Though traditional anodizing has been used successfully, it has its share of disadvantages. Manual adjustments and control of current flow to the part during anodizing not only provides inconsistent and non-reproducible coatings, but increases the risk of defects and rejects. This particularly becomes a problem when anodizing alloys rich in copper (2xxx series) since these alloys are more prone to “burning” on high current density areas. Therefore, extra attention to current control is needed when anodizing these difficult alloys. The use of less efficient lead cathodes and copper bus bars adds to the problem by increasing voltages required to form the oxide and introducing copper contaminates, respectively. As the level of unwanted contaminates in the bath increases, the electrolyte must be disposed of more frequently to maintain proper bath chemistry. This presentation will discuss the advantages of anodizing using the MetalastTM Process Control Technology, which consists of a bath additive and process control equipment for providing optimum and reproducible coatings reducing defects and needless rework.