CHARACTERIZATION OF AA2024-T3 BY SCANNING KELVIN PROBE FORCE MICROSCOPY

Volta potential mapping of AA2024-T3 on surfaces was performed with an atomic force microscope. A linear relation was found between the Volt a potential measured in air and the corrosion potential in aqueous sol ution for a range of pure metal samples, indicating that this potentia l is a measurement of the practical nobility of the surface. Large dif ferences in the Volta potential of intermetallic particles in AA2024-T 3 and the matrix phase resulted in a potential map with high contrast that clearly identifies the location of the particles. All intermetall ic particles, including the Mg-containing S-phase particles, had a Vol ta potential noble to that of the matrix. Surface films on the particl es and the matrix were found to have strong effects on the potential, and probably explain the noble nature of the Mg-containing particles, which have been reported to be active to the matrix in solution. The e ffect of these surface films was examined by refreshing the sample sur face using different techniques. Lateral heterogeneities in certain in termetallic particles were also revealed.