Abstract
Replicate samples of bare aluminum alloy AA7075-T6 were exposed at three coastal atmospheric test sites: Kennedy Space Center (KSC) FL, US Naval Research Laboratory in Key West, FL (NRL-KW), and Daytona Beach, FL. The samples were cross sections of rod stock mounted in standard two-part epoxy metallurgical mounts and wet polished with isopropanol to 600 grit finish. The samples were installed on atmospheric exposure racks and retrieved at intervals of 3, 6, 9, and 12 months. Elemental composition of baseline (non-exposed) and exposed samples were measured using a Zeiss EVO-50XP Environmental Scanning Electron microscope equipped with a EDAX Genesis 2000 energy dispersive X-ray spectroscopy (EDS) system. Pitted and non-pitted sites on each sample were analyzed for compositional elements of the alloy as well as non-compositional elements (i.e. environmentally-derived). It was determined that the deposition of elements in pitted locations on the specimens occurred at concentrations of 200% to 800% to that of major ions present in natural seawater. The deposition and concentration of these environmentally derived elements on the metal surface vary as a function of exposure site and length of exposure time.
