Abstract
Galvanic interaction between the Al alloys 1100, 2024, 2219, 6061, 7075, and Ag, Cu, Ni, Sn, Cd, Zn, the stainless steels 301, 304L, 347, A286, PH13-8Mo, Steel 4130, Inconel 718, Haynes 188 and Ti-6AI-4V has been studied in air saturated 3.5% NaCl by weight loss measurements and continuous monitoring of the galvanic current in 24 hour tests. Results show that the potential difference of uncoupled dissimilar metals, while in most cases accurately predicting the direction of current flow, is a poor indicator of the extent (rate) of galvanic corrosion of coupled dissimilar materials. The values of the average galvanic current density agree well with the increase of dissolution rates due to galvanic coupling. In general, galvanic corrosion of Al alloys coupled to dissimilar metals decreases in the order Ag > Cu > steel 4130 ≫ stainless steels ≈ Ni > Inconel 718 ≫ Ti-6AI-4V ≈ Haynes 188 >Sn > Cd. Coupling to zinc does not result in cathodic protection for all Al alloys studied, but can lead to increased attack as shown by weight loss data. Galvanic series for each Al alloy based on galvanic current data have been established. The results of all 95 couples have also been ranked according to the absolute increase of dissolution rates which is proportional to the average galvanic current density (cd). A ranking based on the relative increase of dissolution rates shows pronounced susceptibility to galvanic corrosion for the Al alloys 1100 and 6061, which have low corrosion rates when not in contact with dissimilar metals. According to the relative increase of dissolution rates which the materials studied cause to Al alloys, they have been placed in three clases (compatible, borderline, and incompatible with Al alloys).
