Galvanic Corrosion Between Nonmetallic Composites and Metals II. Effect of Area Ratio and Environmental Degradation

The effect of cathodic-to-anodic area ratio on the galvanic corrosion induced by graphite-epoxy composite materials (GECMs) coupled to metallic materials (ferrous and nonferrous) in neutral, air-saturated, aqueous 3.5% NaCl solutions has been investigated. Two types of composites were electrically coupled to the aluminum alloys: 2024-T3, 7075-T6, 7075-T73, and 5052; to the stainless steels: 301 1/2H, 302 1/4H, 321, 15-5-PH, and 17-7-PH; to carbon steel 4340, titanium alloy Ti-6Al-4V, and Al-NiBronze alloy. The galvanic corrosion behavior was studied by continuous measurement of the galvanic current using a zero-resistance ammeter in 24-h tests. The effect of environmental degradation of GECMs on the galvanic corrosion of the 7075-T6 alloy has been also addressed in this paper. Results of this investigation indicated that: (1) the galvanic current was found to be independent of the anodic area and directly proportional to the cathodic area when the Al alloys, the 4340 steel, and the Al-NiBronze are coupled to GECMs; (2) the stainless steels and the Ti-6Al-4V alloy, when coupled to GECMs, exhibit galvanic currents that depend on both the anodic and the cathodic areas; and (3) the aging of GECMs in distilled water or in 3.5% NaCl affects the galvanic dissolution of the coupled aluminum alloy 7075-T6.