NAVAL AIR DEVELOPMENT CENTER WARMINSTER PA AIR VEHICLE TECHNOLOGY DEPT
The electrochemical approach was used to show the nature of the galvanic corrosion when graphite-epoxy composite materials are coupled to aluminum and titanium alloys. An open circuit potential difference of one volt was obtained in 3.5 NaCl solution between the composite and 7075-T6, 7075-T651 and 5052-H38 alloys. This potential difference provides a driving force for corrosion and is cause for concern. The Ti-6-4 showed a difference of about 0.3 volt for the unpolished as received material. Corrosion current data zero impedance technique indicate that aluminum alloys and cadmium plate are much more reactive than Ti-6-4 when coupled to graphite-epoxy. This technique provides a means of ranking the severity of this corrosion problem for various aircraft alloys. Flatwise tensile data indicate significant strength losses when graphite-epoxy composite sandwich specimens are exposed to ASTM 5 salt spray and synthetic sea water SO2 spray environments.