The corrosion potential of an aluminum alloy depends upon the amounts of certain alloying elements that the alloy contains in solid solution. Copper and zinc, which are two of the major alloying elements for aluminum, have the greatest effect with copper shifting the potential in the noble or positive direction, and zinc in the active or negative direction. For example, commercially unalloyed aluminum (1100 alloy) has a potential of -750 mV when measured in accordance with this method, 2024-T3 alloy with nearly all of its nominal 4.3 % copper in solid solution, a potential of -600 to -620 mV, depending upon the rate of quenching and 7072 alloy with nearly all of its nominal 1.0 % zinc in solid solution, a potential of 885 mV (SCE) (1-3).

Because it reflects the amount of certain alloying elements in solid solution, the corrosion potential is a useful tool for characterizing the metallurgical condition of aluminum alloys, especially those of the 2XXX and 7XXX types, which contain copper and zinc as major alloying elements. Its uses include the determination of the effectiveness of solution heat treatment and annealing (1), of the extent of precipitation during artificial aging (4) and welding (5), and of the extent of diffusion of alloying elements from the core into the cladding of Alclad products (2).