GALVANIC CORROSION BETWEEN NONMETALLIC COMPOSITES AND METALS .1. EFFECT OF METAL AND OF TEMPERATURE

Galvanic corrosion induced by plastic composite materials (graphite-epoxy-composite-materials, GECMs) coupled to metallic materials (ferrous and nonferrous) in neutral and air-saturated aqueous 3.5% NaCl solution has been investigated. Two types of composites, manufactured by Fiberite and Ciba-Geigy, were electrically coupled to the aluminum alloys 2024-T3, 7075-T6, 7075-T73, and 5052, to the stainless steels 301 1/2 H, 302 1/4 H, 321, 15-5PH, and 17-7PH, to the steel 4340, to Ti-6Al-4V, and to an Al-Ni-Bronze alloy. The galvanic corrosion behavior was studied by continuous measurement of the galvanic current. by weight loss measurements, and by potentiostatic polarization curves for the metallic and nonmetallic materials investigated. Experimental results show that the galvanic corrosion current decreases with the nature of the metal in the following order: 5052 almost-equal-to 7075-T6 > almost-equal-to 4340 > 7075-T73 > 2024-T3 > Al-Ni- Bronze > 321 > 15-5PH > 17-7PH > 302 1/4H > Ti-6Al-4V almost-equal-to 301 1/2H. The potential difference of uncoupled dissimilar materials was found to be a poor predictor of galvanic corrosion rates. Dissolution rates calculated from galvanic data and weight loss data have been analyzed according to a theoretical computation reported in the literature based on mixed potential theory. A satisfactory agreement between theory and experimental findings was found. Galvanic corrosion can be increased by increasing the temperature. An activation energy equal to 5.8 Kcal mole-1 was calculated in the case of the 7075-T6/GECM couple.