General Corrosion

The general corrosion behavior of aluminum alloys depends basically on three factors: (1) the stability of the oxide film, (2) the environment, and (3) the alloying elements; these factors are not independent of one another. The oxide film is considered stable between pH 4.5 and 9.0; however, aluminum can be attacked by certain anions and cations in neutral solutions, and it is resistant to some acids and alkalis.

In general, aluminum alloys have good corrosion resistance in the following environments: atmosphere, most fresh waters, seawater, most soils, most foods, and many chemicals. Since ‘‘good corrosion resistance’’ is intended to mean that the material will give long service life without surface protection, in support of this rating is the following list of established applications of aluminum in various environments:

In Atmosphere. Roofing and siding, truck and aircraft skin, architectural.

With Most Fresh Waters. Storage tanks, pipelines, heat exchangers, pleasure boats.

In Seawater. Ship hulls and superstructures, buoys, pipelines.

In Soils. Pipelines and drainage pipes.

With Foods. Cooking utensils, tanks and equipment, cans and packaging.

With Chemicals. Storage tanks, processing and transporting equipment.

It is generally true that the higher the aluminum purity, the greater is its corrosion resistance. However, certain elements can be alloyed with aluminum without reducing its corrosion resistance and in some cases an improvement actually results. Those elements having little or no effect include Mn, Mg, Zn, Si, Sb, Bi, Pb, and Ti; those having a detrimental effect include Cu, Fe, and Ni. Some guidelines for the different alloy groupings

include the following:

Al–Mn Alloys. Al–Mn alloys (3xxx series) have good corrosion resistance and may possibly be better than 1100 alloy in marine environments and for cooking utensils because of a reduced effect by Fe in these alloys.

Al–Mg Alloys. Al–Mg alloys (5xxx series) are as corrosion resistant as 1xxx alloys and even more resistant to salt water and some alkaline solutions. In general, they offer the best combination of strength and corrosion resistance of all aluminum alloys.

Al–Mg–Si Alloys. Al–Mg–Si alloys (6xxx series) have good resistance to atmosphere corrosion but generally slightly lower resistance than Al–Mg alloys. They can be used unprotected in most atmospheres and waters.
Alclad Alloys. Alclad alloys are composite wrought products comprised of an aluminum alloy core with a thin layer of corrosion—protective pure aluminum or aluminum alloy metallurgically bonded to one or both surfaces of the core. As a class, alclad alloys have a very high resistance to corrosion. The cladding is anodic to the core
and thus protects the core.






J. G. Kaufman
Kaufman Associates
Columbus, Ohio

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright  2006 by John Wiley & Sons, Inc.

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