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Friday, February 01, 2008

Cleaning Aluminum

How is galvanic corrosion prevented when cleaning aluminum?

Aluminum is an active metal that is somewhat high on the "anodic index" of the galvanic series. If aluminum is cleaned with other metals present, you can create a battery and get galvanic corrosion. Aluminum should not be cleaned in the presence of metals that are significantly higher or lower on the anodic series; higher on the anodic scale such as zinc, magnesium or beryllium metals and lower on the anodic scale such as tin, brass, bronze, copper, silver, nickel and rhodium. Galvanic corrosion is facilitated between aluminum and other metals that may be dissolved in the cleaning bath from prior cleaning, or present in the cleaning bath during the time of cleaning. The corrosion can take the form of a dark grey film or deposit, a brown film or deposit, and with more exotic metals, other colors are possible. Certain cast alloys of aluminum can have galvanic corrosion problems with cast iron, carbon steel and low alloy steels. Note that intact and properly passivated stainless steel does not have a problem with galvanic corrosion on aluminum during normal cleaning.

The Alconox brand cleaners recommended for cleaning aluminum are Alconox, Liquinox, Tergazyme, Alcojet, Alcotabs, Detojet, Citranox, Luminox, Citrajet, Solujet and Tergajet. Detergent 8 is not recommended for cleaning aluminum. Aluminum that has been exposed to the environment often forms a characteristic dull grey surface oxide. None of the recommended cleaners will remove this and brighten the aluminum again. The recommended cleaners are intended for use in removing residues, not surface oxides that are bound in to the aluminum matrix. To clean this type of aluminum, there are very hazardous strong acid cleaners that can sometimes be effective. Alternatively, there are mild abrasive cleaners that can be used to polish the dark coating off the aluminum surface. Alconox does not make any of these kinds of cleaners.

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