Laboratory Studies of Galvanic Corrosion of Aluminum Alloys

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Abstract
In a systematic study of galvanic corrosion of aluminum alloys the effects of the dissimilar metal, the solution composition, and area ratio have been evaluated using galvanic current and weight loss measurements. In 3.5 percent sodium chloride, galvanic corrosion rates of the aluminum alloys 1100, 2024, 2219, 6061, and 7075 decrease with the nature of the dissimilar metal in the order: silver > copper > 4130 steel ≫ stainless steel ≈ nickel > Inconel 718 ≫ Ti-6Al-4V ≈ Haynes 188 > tin > cadmium. Coupling to zinc did not lead to cathodic protection of the aluminum alloys as shown by weight loss data, although the aluminum alloys were the cathode in the aluminum-zinc couple. The potential difference of uncoupled dissimilar metals has been found to be a poor indicator of galvanic corrosion rates. Dissolution rates of aluminum alloys coupled to a given dissimilar material are higher in 3.5 percent sodium chloride than in tap water and distilled water where they are found to be comparable. The effect of area ratio AC/AA has been studied in 3.5 percent sodium chloride for area ratios of 0.1, 1.0, or 10. The galvanic curent was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density has been studied in 3.5 percent sodium chloride for area ratios of 0.1, 1.0, or 10. The galvanic curent was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density igA with respect to the anode has been found to be directly proportional to the area ratio (with respect to the anode has been found to be directly proportional to the area ratio (igA = = k1 AC/AA), while the dissolution rate), while the dissolution rate rA of the anode was related to area area ratio by rA = k2 (1 + AC/AA). The results obtained have been explained based on mixed potential theory. Electrochemical methods for measurements of galvanic currents are described in the Appendix.
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