Mechanism of Intergranular Corrosion in 2XXX Alloys

Plot of corrosion potentials of pure aluminum and binary aluminum plus copper alloys, plus the two stoichiometric precipitates. The binary alloys were fully solution heat treated and quenched as rapidly as possible to retain the maximum amount of copper in solid solution. Note that the addition of copper raises the corrosion potential of pure aluminum by about 0.14 V. (Courtesy of Alcoa Technical Center, Marsha Egbert.) 

15 V can exist between pure aluminum and Al + 4% (or more) dissolved copper. 

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